Remove calls to some POSIX APIs which Fuchsia does not implement.

Fuchsia's POSIX-lite does not provide the pthread priority nor file
locking APIs.

Bug: chromium:809201
Change-Id: I1efc5fe46909771e4934d91d2ed5f3e97c33444c
Reviewed-on: https://webrtc-review.googlesource.com/48860
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Commit-Queue: Wez <wez@google.com>
Cr-Commit-Position: refs/heads/master@{#21990}

rtc_base/platform_thread.cc

@@ -297,8 +297,8 @@ bool PlatformThread::SetPriority(ThreadPriority priority) {
 
 #if defined(WEBRTC_WIN)
   return SetThreadPriority(thread_, priority) != FALSE;
-#elif defined(__native_client__)
-  // Setting thread priorities is not supported in NaCl.
+#elif defined(__native_client__) || defined(WEBRTC_FUCHSIA)
+  // Setting thread priorities is not supported in NaCl or Fuchsia.
   return true;
 #elif defined(WEBRTC_CHROMIUM_BUILD) && defined(WEBRTC_LINUX)
   // TODO(tommi): Switch to the same mechanism as Chromium uses for changing

rtc_base/stream.cc

@@ -481,30 +481,6 @@ bool FileStream::Flush() {
   return false;
 }
 
-#if defined(WEBRTC_POSIX) && !defined(__native_client__)
-
-bool FileStream::TryLock() {
-  if (file_ == nullptr) {
-    // Stream not open.
-    RTC_NOTREACHED();
-    return false;
-  }
-
-  return flock(fileno(file_), LOCK_EX|LOCK_NB) == 0;
-}
-
-bool FileStream::Unlock() {
-  if (file_ == nullptr) {
-    // Stream not open.
-    RTC_NOTREACHED();
-    return false;
-  }
-
-  return flock(fileno(file_), LOCK_UN) == 0;
-}
-
-#endif
-
 void FileStream::DoClose() {
   fclose(file_);
 }

rtc_base/stream.h

@@ -400,13 +400,6 @@ class FileStream : public StreamInterface {
 
   bool Flush() override;
 
-#if defined(WEBRTC_POSIX) && !defined(__native_client__)
-  // Tries to aquire an exclusive lock on the file.
-  // Use OpenShare(...) on win32 to get similar functionality.
-  bool TryLock();
-  bool Unlock();
-#endif
-
  protected:
   virtual void DoClose();