Revert of Introduce an IsMutable method on VideoFrameBuffer. (patchset #1 id:1 of https://codereview.webrtc.org/1881933004/ )

Reason for revert:
This is breaking all FYI bots.
The new virtual method is not implemented on the Chromium side yet.

Original issue's description:
> Introduce an IsMutable method on VideoFrameBuffer.
>
> Unlike HasOneRef, it can be overridden to always return false in
> immutable subclasses.
>
> I'm also investigating overiding it in PooledI420Buffer, to directly
> inherit I420Buffer but ignore the reference from the pool. Still
> unclear if that will work out.
>
> BUG=webrtc:5682
>
> Committed: https://crrev.com/6bd10f2c1ac912cbe5addd880e559d59274c60e6
> Cr-Commit-Position: refs/heads/master@{#12365}

TBR=magjed@webrtc.org,perkj@webrtc.org,pbos@webrtc.org,nisse@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:5682

Review URL: https://codereview.webrtc.org/1885943004

Cr-Commit-Position: refs/heads/master@{#12366}

webrtc/common_video/i420_buffer_pool.cc

@@ -29,11 +29,10 @@ class PooledI420Buffer : public webrtc::VideoFrameBuffer {
   const uint8_t* data(webrtc::PlaneType type) const override {
     return buffer_->data(type);
   }
-  bool IsMutable() { return HasOneRef(); }
   uint8_t* MutableData(webrtc::PlaneType type) override {
     // Make the HasOneRef() check here instead of in |buffer_|, because the pool
     // also has a reference to |buffer_|.
-    RTC_DCHECK(IsMutable());
+    RTC_DCHECK(HasOneRef());
     return const_cast<uint8_t*>(buffer_->data(type));
   }
   int stride(webrtc::PlaneType type) const override {
@@ -81,7 +80,7 @@ rtc::scoped_refptr<VideoFrameBuffer> I420BufferPool::CreateBuffer(int width,
     // CreateBuffer that has not been released yet. If the ref count is 1
     // (HasOneRef), then the list we are looping over holds the only reference
     // and it's safe to reuse.
-    if (buffer->IsMutable())
+    if (buffer->HasOneRef())
       return new rtc::RefCountedObject<PooledI420Buffer>(buffer);
   }
   // Allocate new buffer.

webrtc/common_video/i420_buffer_pool_unittest.cc

@@ -55,7 +55,7 @@ TEST(TestI420BufferPool, ExclusiveOwner) {
   // Check that created buffers are exclusive so that they can be written to.
   I420BufferPool pool;
   rtc::scoped_refptr<VideoFrameBuffer> buffer = pool.CreateBuffer(16, 16);
-  EXPECT_TRUE(buffer->IsMutable());
+  EXPECT_TRUE(buffer->HasOneRef());
 }
 
 TEST(TestI420BufferPool, FrameValidAfterPoolDestruction) {
@@ -64,7 +64,7 @@ TEST(TestI420BufferPool, FrameValidAfterPoolDestruction) {
     I420BufferPool pool;
     buffer = pool.CreateBuffer(16, 16);
   }
-  EXPECT_TRUE(buffer->IsMutable());
+  EXPECT_TRUE(buffer->HasOneRef());
   EXPECT_EQ(16, buffer->width());
   EXPECT_EQ(16, buffer->height());
   // Try to trigger use-after-free errors by writing to y-plane.

webrtc/common_video/include/video_frame_buffer.h

@@ -33,13 +33,7 @@ enum PlaneType {
 // 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 @@ class I420Buffer : public VideoFrameBuffer {
   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 @@ class NativeHandleBuffer : public VideoFrameBuffer {
   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_;
@@ -139,8 +131,6 @@ class WrappedI420Buffer : public webrtc::VideoFrameBuffer {
   int width() const override;
   int height() const override;
 
-  bool IsMutable() override;
-
   const uint8_t* data(PlaneType type) const override;
 
   int stride(PlaneType type) const override;

webrtc/common_video/video_frame.cc

@@ -65,7 +65,7 @@ void VideoFrame::CreateEmptyFrame(int width,
   rotation_ = kVideoRotation_0;
 
   // Check if it's safe to reuse allocation.
-  if (video_frame_buffer_ && video_frame_buffer_->IsMutable() &&
+  if (video_frame_buffer_ && video_frame_buffer_->HasOneRef() &&
       !video_frame_buffer_->native_handle() &&
       width == video_frame_buffer_->width() &&
       height == video_frame_buffer_->height() && stride_y == stride(kYPlane) &&

webrtc/common_video/video_frame_buffer.cc

@@ -89,12 +89,8 @@ const uint8_t* I420Buffer::data(PlaneType type) const {
   }
 }
 
-bool I420Buffer::IsMutable() {
-  return HasOneRef();
-}
-
 uint8_t* I420Buffer::MutableData(PlaneType type) {
-  RTC_DCHECK(IsMutable());
+  RTC_DCHECK(HasOneRef());
   return const_cast<uint8_t*>(
       static_cast<const VideoFrameBuffer*>(this)->data(type));
 }
@@ -148,10 +144,6 @@ NativeHandleBuffer::NativeHandleBuffer(void* native_handle,
   RTC_DCHECK_GT(height, 0);
 }
 
-bool NativeHandleBuffer::IsMutable() {
-  return false;
-}
-
 int NativeHandleBuffer::width() const {
   return width_;
 }
@@ -198,11 +190,6 @@ WrappedI420Buffer::~WrappedI420Buffer() {
   no_longer_used_cb_();
 }
 
-// Data owned by creator; never mutable.
-bool WrappedI420Buffer::IsMutable() {
-  return false;
-}
-
 int WrappedI420Buffer::width() const {
   return width_;
 }

webrtc/media/engine/webrtcvideoframe.cc

@@ -119,7 +119,7 @@ int32_t WebRtcVideoFrame::GetVPitch() const {
 }
 
 bool WebRtcVideoFrame::IsExclusive() const {
-  return video_frame_buffer_->IsMutable();
+  return video_frame_buffer_->HasOneRef();
 }
 
 void* WebRtcVideoFrame::GetNativeHandle() const {