Merge system_wrappers:metrics and system_wrappers:metrics_default.

After this CL, WebRTC clients will be able to exclude the default
metrics implementation by defining the preprocessor macro
WEBRTC_EXCLUDE_METRICS_DEFAULT (if GN is used, it will be enough
to set rtc_exclude_metrics_default to true).

Bug: webrtc:9631
Change-Id: Id6db23cc4b6c292d9f97372a8014c0c467ed0538
No-Try: True
Reviewed-on: https://webrtc-review.googlesource.com/98102
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24747}

system_wrappers/BUILD.gn

@@ -110,18 +110,6 @@ rtc_source_set("runtime_enabled_features_api") {
   ]
 }
 
-rtc_source_set("metrics_api") {
-  visibility = [ "*" ]
-  sources = [
-    "include/metrics.h",
-  ]
-  deps = [
-    "..:webrtc_common",
-    "../rtc_base:checks",
-    "../rtc_base:rtc_base_approved",
-  ]
-}
-
 rtc_source_set("field_trial_default") {
   visibility = [ "*" ]
   sources = [
@@ -145,15 +133,40 @@ rtc_source_set("runtime_enabled_features_default") {
   ]
 }
 
+rtc_source_set("metrics") {
+  visibility = [ "*" ]
+  public = [
+    "include/metrics.h",
+    "include/metrics_default.h",
+  ]
+  sources = [
+    "source/metrics.cc",
+  ]
+  if (rtc_exclude_metrics_default) {
+    defines = [ "WEBRTC_EXCLUDE_METRICS_DEFAULT" ]
+  }
+  deps = [
+    "..:webrtc_common",
+    "../rtc_base:checks",
+    "../rtc_base:rtc_base_approved",
+  ]
+}
+
+# TODO(bugs.webrtc.org/9631): Remove this as soon as Chromium stops depending
+# on it.
+rtc_source_set("metrics_api") {
+  visibility = [ "*" ]
+  public_deps = [  # no-presubmit-check TODO(webrtc:8603)
+    ":metrics",
+  ]
+}
+
+# TODO(bugs.webrtc.org/9631): Remove this as soon as Chromium stops depending
+# on it.
 rtc_source_set("metrics_default") {
   visibility = [ "*" ]
-  sources = [
+  public_deps = [  # no-presubmit-check TODO(webrtc:8603)
-    "include/metrics_default.h",
+    ":metrics",
-    "source/metrics_default.cc",
-  ]
-  deps = [
-    ":metrics_api",
-    "../rtc_base:rtc_base_approved",
   ]
 }
 

system_wrappers/include/metrics.h

@@ -11,6 +11,8 @@
 #ifndef SYSTEM_WRAPPERS_INCLUDE_METRICS_H_
 #define SYSTEM_WRAPPERS_INCLUDE_METRICS_H_
 
+#include <map>
+#include <memory>
 #include <string>
 
 #include "common_types.h"  // NOLINT(build/include)
@@ -31,20 +33,21 @@
 // The macros use the methods HistogramFactoryGetCounts,
 // HistogramFactoryGetEnumeration and HistogramAdd.
 //
-// Therefore, WebRTC clients must either:
+// By default WebRTC provides implementations of the aforementioned methods
-//
+// that can be found in system_wrappers/source/metrics.cc. If clients want to
-// - provide implementations of
+// provide a custom version, they will have to:
-//   Histogram* webrtc::metrics::HistogramFactoryGetCounts(
-//       const std::string& name, int sample, int min, int max,
-//       int bucket_count);
-//   Histogram* webrtc::metrics::HistogramFactoryGetEnumeration(
-//       const std::string& name, int sample, int boundary);
-//   void webrtc::metrics::HistogramAdd(
-//       Histogram* histogram_pointer, const std::string& name, int sample);
-//
-// - or link with the default implementations (i.e.
-//   system_wrappers:metrics_default).
 //
+// 1. Compile WebRTC defining the preprocessor macro
+//    WEBRTC_EXCLUDE_METRICS_DEFAULT (if GN is used this can be achieved
+//    by setting the GN arg rtc_exclude_metrics_default to true).
+// 2. Provide implementations of:
+//    Histogram* webrtc::metrics::HistogramFactoryGetCounts(
+//        const std::string& name, int sample, int min, int max,
+//        int bucket_count);
+//    Histogram* webrtc::metrics::HistogramFactoryGetEnumeration(
+//        const std::string& name, int sample, int boundary);
+//    void webrtc::metrics::HistogramAdd(
+//        Histogram* histogram_pointer, const std::string& name, int sample);
 //
 // Example usage:
 //
@@ -274,6 +277,39 @@ Histogram* SparseHistogramFactoryGetEnumeration(const std::string& name,
 // Function for adding a |sample| to a histogram.
 void HistogramAdd(Histogram* histogram_pointer, int sample);
 
+struct SampleInfo {
+  SampleInfo(const std::string& name, int min, int max, size_t bucket_count);
+  ~SampleInfo();
+
+  const std::string name;
+  const int min;
+  const int max;
+  const size_t bucket_count;
+  std::map<int, int> samples;  // <value, # of events>
+};
+
+// Enables collection of samples.
+// This method should be called before any other call into webrtc.
+void Enable();
+
+// Gets histograms and clears all samples.
+void GetAndReset(
+    std::map<std::string, std::unique_ptr<SampleInfo>>* histograms);
+
+// Functions below are mainly for testing.
+
+// Clears all samples.
+void Reset();
+
+// Returns the number of times the |sample| has been added to the histogram.
+int NumEvents(const std::string& name, int sample);
+
+// Returns the total number of added samples to the histogram.
+int NumSamples(const std::string& name);
+
+// Returns the minimum sample value (or -1 if the histogram has no samples).
+int MinSample(const std::string& name);
+
 }  // namespace metrics
 }  // namespace webrtc
 

system_wrappers/include/metrics_default.h

@@ -11,51 +11,6 @@
 #ifndef SYSTEM_WRAPPERS_INCLUDE_METRICS_DEFAULT_H_
 #define SYSTEM_WRAPPERS_INCLUDE_METRICS_DEFAULT_H_
 
-#include <map>
+#include "system_wrappers/include/metrics.h"
-#include <memory>
-#include <string>
-
-namespace webrtc {
-namespace metrics {
-
-// This class does not actually exist. It is casted to an implementation defined
-// pointer inside the functions.
-class Histogram;
-
-struct SampleInfo {
-  SampleInfo(const std::string& name, int min, int max, size_t bucket_count);
-  ~SampleInfo();
-
-  const std::string name;
-  const int min;
-  const int max;
-  const size_t bucket_count;
-  std::map<int, int> samples;  // <value, # of events>
-};
-
-// Enables collection of samples.
-// This method should be called before any other call into webrtc.
-void Enable();
-
-// Gets histograms and clears all samples.
-void GetAndReset(
-    std::map<std::string, std::unique_ptr<SampleInfo>>* histograms);
-
-// Functions below are mainly for testing.
-
-// Clears all samples.
-void Reset();
-
-// Returns the number of times the |sample| has been added to the histogram.
-int NumEvents(const std::string& name, int sample);
-
-// Returns the total number of added samples to the histogram.
-int NumSamples(const std::string& name);
-
-// Returns the minimum sample value (or -1 if the histogram has no samples).
-int MinSample(const std::string& name);
-
-}  // namespace metrics
-}  // namespace webrtc
 
 #endif  // SYSTEM_WRAPPERS_INCLUDE_METRICS_DEFAULT_H_

system_wrappers/source/metrics.cc

@@ -7,13 +7,12 @@
 // be found in the AUTHORS file in the root of the source tree.
 //
 
-#include "system_wrappers/include/metrics_default.h"
+#include "system_wrappers/include/metrics.h"
 
 #include <algorithm>
 
 #include "rtc_base/criticalsection.h"
 #include "rtc_base/thread_annotations.h"
-#include "system_wrappers/include/metrics.h"
 
 // Default implementation of histogram methods for WebRTC clients that do not
 // want to provide their own implementation.
@@ -203,6 +202,7 @@ RtcHistogramMap* GetMap() {
 }
 }  // namespace
 
+#ifndef WEBRTC_EXCLUDE_METRICS_DEFAULT
 // Implementation of histogram methods in
 // webrtc/system_wrappers/interface/metrics.h.
 
@@ -259,6 +259,8 @@ void HistogramAdd(Histogram* histogram_pointer, int sample) {
   ptr->Add(sample);
 }
 
+#endif  // WEBRTC_EXCLUDE_METRICS_DEFAULT
+
 SampleInfo::SampleInfo(const std::string& name,
                        int min,
                        int max,