Android: Add interface for getting native EGL context

This CL also implements support for getting the native context on
EGL 1.4. It's a bit tricker to get the native handle for EGL 1.0 so it
will be done in a separate CL.

Bug: webrtc:8257
Change-Id: I269e75c357f19507098180077fa9d1b1ac4dce23
Reviewed-on: https://webrtc-review.googlesource.com/1880
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Commit-Queue: Magnus Jedvert <magjed@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#19890}

sdk/android/api/org/webrtc/EglBase.java

@@ -21,7 +21,7 @@ import javax.microedition.khronos.egl.EGL10;
  */
 public abstract class EglBase {
   // EGL wrapper for an actual EGLContext.
-  public static class Context {}
+  public interface Context { long getNativeEglContext(); }
 
   // According to the documentation, EGL can be used from multiple threads at the same time if each
   // thread has its own EGLContext, but in practice it deadlocks on some devices when doing this.

sdk/android/src/java/org/webrtc/EglBase10.java

@@ -37,9 +37,18 @@ class EglBase10 extends EglBase {
   private EGLSurface eglSurface = EGL10.EGL_NO_SURFACE;
 
   // EGL wrapper for an actual EGLContext.
-  public static class Context extends EglBase.Context {
+  public static class Context implements EglBase.Context {
     private final EGLContext eglContext;
 
+    @Override
+    public long getNativeEglContext() {
+      // TODO(magjed): Implement. There is no easy way of getting the native context for EGL 1.0. We
+      // need to make sure to have an EglSurface, then make the context current using that surface,
+      // and then call into JNI and call the native version of eglGetCurrentContext. Then we need to
+      // restore the state and return the native context.
+      throw new RuntimeException("getNativeEglContext is not implemented for EGL 1.0");
+    }
+
     public Context(EGLContext eglContext) {
       this.eglContext = eglContext;
     }

sdk/android/src/java/org/webrtc/EglBase14.java

@@ -43,9 +43,17 @@ class EglBase14 extends EglBase {
     return (CURRENT_SDK_VERSION >= EGLExt_SDK_VERSION);
   }
 
-  public static class Context extends EglBase.Context {
+  public static class Context implements EglBase.Context {
     private final android.opengl.EGLContext egl14Context;
 
+    @Override
+    @SuppressWarnings("deprecation")
+    public long getNativeEglContext() {
+      return CURRENT_SDK_VERSION >= android.os.Build.VERSION_CODES.LOLLIPOP
+          ? egl14Context.getNativeHandle()
+          : egl14Context.getHandle();
+    }
+
     public Context(android.opengl.EGLContext eglContext) {
       this.egl14Context = eglContext;
     }