Allow media track switching.

media/video/gpu_memory_buffer_video_frame_pool.h

Index: media/video/gpu_memory_buffer_video_frame_pool.h
diff --git a/media/video/gpu_memory_buffer_video_frame_pool.h b/media/video/gpu_memory_buffer_video_frame_pool.h
index ed4b3617e53cd39b0cf78d7f7dd7e6b9d16ddd47..b7c16b5a1aa8affcf552641191c90897c3ca5b07 100644
--- a/media/video/gpu_memory_buffer_video_frame_pool.h
+++ b/media/video/gpu_memory_buffer_video_frame_pool.h
@@ -24,6 +24,11 @@ class GpuVideoAcceleratorFactories;
 // The pool recycles resources to a void unnecessarily allocating and
 // destroying textures, images and GpuMemoryBuffer that could result
 // in a round trip to the browser/GPU process.
+// NOTE: Destroying the pool will not immediately invalidate outstanding video
+// frames. GPU memory buffers will be kept alive by video frames indirectly
+// referencing them. Video frames themselves are ref-counted and will be
+// released when they are no longer needed, potentially after the pool is
+// destroyed.
 class MEDIA_EXPORT GpuMemoryBufferVideoFramePool {
  public:
   GpuMemoryBufferVideoFramePool();