Implement evictFrames() to support MSE's coded frame eviction algorithm.

media/filters/source_buffer_stream.h

Index: media/filters/source_buffer_stream.h
diff --git a/media/filters/source_buffer_stream.h b/media/filters/source_buffer_stream.h
index 362a9ab6272f49d9a9f33f6af8f9da870397814e..d516a6a41918a6e76b941b590605ee7dafa724a2 100644
--- a/media/filters/source_buffer_stream.h
+++ b/media/filters/source_buffer_stream.h
@@ -89,6 +89,9 @@ class MEDIA_EXPORT SourceBufferStream {
   void Remove(base::TimeDelta start, base::TimeDelta end,
               base::TimeDelta duration);
 
+  // Frees up space if the SourceBufferStream is taking up too much memory.
+  bool GarbageCollectIfNeeded();
+
   // Changes the SourceBufferStream's state so that it will start returning
   // buffers starting from the closest keyframe before |timestamp|.
   void Seek(base::TimeDelta timestamp);
@@ -149,9 +152,6 @@ class MEDIA_EXPORT SourceBufferStream {
  private:
   friend class SourceBufferStreamTest;
 
-  // Frees up space if the SourceBufferStream is taking up too much memory.
-  void GarbageCollectIfNeeded();
-
   // Attempts to delete approximately |total_bytes_to_free| amount of data
   // |ranges_|, starting at the front of |ranges_| and moving linearly forward
   // through the buffers. Deletes starting from the back if |reverse_direction|