Revert of Introduce an IsMutable method on VideoFrameBuffer.

webrtc/common_video/include/video_frame_buffer.h

Index: webrtc/common_video/include/video_frame_buffer.h
diff --git a/webrtc/common_video/include/video_frame_buffer.h b/webrtc/common_video/include/video_frame_buffer.h
index f1b78492baf2f9cadaecb6a243c33cf5460229b0..9cf57a43591b1da66f82ed9d59ffde5794fdc212 100644
--- a/webrtc/common_video/include/video_frame_buffer.h
+++ b/webrtc/common_video/include/video_frame_buffer.h
@@ -33,13 +33,7 @@
 // not contain any frame metadata such as rotation, timestamp, pixel_width, etc.
 class VideoFrameBuffer : public rtc::RefCountInterface {
  public:
-  // Returns true if the caller is exclusive owner, and allowed to
-  // call MutableData.
-  virtual bool IsMutable() = 0;
-
-  // Underlying refcount access, used to implement IsMutable.
-  // TODO(nisse): Demote to protected, as soon as Chrome is changed to
-  // use IsMutable.
+  // Returns true if this buffer has a single exclusive owner.
   virtual bool HasOneRef() const = 0;
 
   // The resolution of the frame in pixels. For formats where some planes are
@@ -82,7 +76,6 @@
   const uint8_t* data(PlaneType type) const override;
   // Non-const data access is only allowed if HasOneRef() is true to protect
   // against unexpected overwrites.
-  bool IsMutable() override;
   uint8_t* MutableData(PlaneType type) override;
   int stride(PlaneType type) const override;
   void* native_handle() const override;
@@ -117,7 +110,6 @@
   const uint8_t* data(PlaneType type) const override;
   int stride(PlaneType type) const override;
   void* native_handle() const override;
-  bool IsMutable() override;
 
  protected:
   void* native_handle_;
@@ -138,8 +130,6 @@
                     const rtc::Callback0<void>& no_longer_used);
   int width() const override;
   int height() const override;
-
-  bool IsMutable() override;
 
   const uint8_t* data(PlaneType type) const override;