Remove "mixin" from BeginFrameSource/Observer base classes.

content/browser/android/in_process/synchronous_compositor_external_begin_frame_source.h

Index: content/browser/android/in_process/synchronous_compositor_external_begin_frame_source.h
diff --git a/content/browser/android/in_process/synchronous_compositor_external_begin_frame_source.h b/content/browser/android/in_process/synchronous_compositor_external_begin_frame_source.h
index ee82f70a27c78bae09505ec665d6a0725781bf34..eb7e84b87e645bc28b692db4191654a57d4f32de 100644
--- a/content/browser/android/in_process/synchronous_compositor_external_begin_frame_source.h
+++ b/content/browser/android/in_process/synchronous_compositor_external_begin_frame_source.h
@@ -15,7 +15,7 @@ class SynchronousCompositorImpl;
 // Make sure that this is initialized and set to compositor before output
 // surface is bound to compositor.
 class SynchronousCompositorExternalBeginFrameSource
-    : public cc::BeginFrameSourceMixIn {
+    : public cc::BeginFrameSourceBase {
  public:
   explicit SynchronousCompositorExternalBeginFrameSource(int routing_id);
   ~SynchronousCompositorExternalBeginFrameSource() override;
@@ -23,7 +23,7 @@ class SynchronousCompositorExternalBeginFrameSource
   void BeginFrame(const cc::BeginFrameArgs& args);
   void SetCompositor(SynchronousCompositorImpl* compositor);
 
-  // cc::BeginFrameSourceMixIn implementation.
+  // cc::BeginFrameSourceBase implementation.
   void OnNeedsBeginFramesChange(bool needs_begin_frames) override;
   void SetClientReady() override;