rendering_helper - Drop frames if the decoder cannot catch up.

Originally, we delayed the rendering and waited for the late coming frames. However, when play with audio, the late coming frame should be just dropped to keep the AV sync. So we change to drop a frame if it comes too late.

BUG=411123
TEST=Run vda_unittest on peach_pit.

Review URL: https://codereview.chromium.org/562173003

Cr-Commit-Position: refs/heads/master@{#294992}

content/common/gpu/media/rendering_helper.cc

@@ -75,7 +75,7 @@ VideoFrameTexture::~VideoFrameTexture() {
 }
 
 RenderingHelper::RenderedVideo::RenderedVideo()
-    : last_frame_rendered(false), is_flushing(false) {
+    : last_frame_rendered(false), is_flushing(false), frames_to_drop(0) {
 }
 
 RenderingHelper::RenderedVideo::~RenderedVideo() {
@@ -398,6 +398,11 @@ void RenderingHelper::QueueVideoFrame(
   RenderedVideo* video = &videos_[window_id];
   DCHECK(!video->is_flushing);
 
+  if (video->frames_to_drop > 0) {
+    --video->frames_to_drop;
+    return;
+  }
+
   // Pop the last frame if it has been rendered.
   if (video->last_frame_rendered) {
     // When last_frame_rendered is true, we should have only one pending frame.
@@ -525,6 +530,9 @@ void RenderingHelper::RenderContent() {
       GLSetViewPort(video->render_area);
       RenderTexture(frame->texture_target(), frame->texture_id());
 
+      if (video->last_frame_rendered)
+        ++video->frames_to_drop;
+
       if (video->pending_frames.size() > 1 || video->is_flushing) {
         frames_to_be_returned.push_back(video->pending_frames.front());
         video->pending_frames.pop();

content/common/gpu/media/rendering_helper.h

@@ -134,6 +134,9 @@ class RenderingHelper {
     // True if there won't be any new video frames comming.
     bool is_flushing;
 
+    // The number of frames need to be dropped to catch up the rendering.
+    int frames_to_drop;
+
     // The video frames pending for rendering.
     std::queue<scoped_refptr<VideoFrameTexture> > pending_frames;