Tweak multibuffer buffering strategy.

media/blink/multibuffer_reader.h

Index: media/blink/multibuffer_reader.h
diff --git a/media/blink/multibuffer_reader.h b/media/blink/multibuffer_reader.h
index 19e90617f76ae4f07101927bef962d6bbdbc09ef..cd64982086dcb4d721a5cae35964cc20f3141823 100644
--- a/media/blink/multibuffer_reader.h
+++ b/media/blink/multibuffer_reader.h
@@ -78,7 +78,12 @@ class MEDIA_BLINK_EXPORT MultiBufferReader
   // The range [current_position - backward ... current_position + forward)
   // will be locked in the cache. Calling Wait() or TryRead() with values
   // larger than |forward| is not supported.
-  void SetMaxBuffer(int64_t backward, int64_t forward);
+  void SetPinRange(int64_t backward, int64_t forward);
+
+  // Set how much memory usage we target. This memory is added to the global
+  // LRU and shared between all multibuffers. We may end up using more memory
+  // if no memory can be freed due to pinning.
+  void SetMaxBuffer(int64_t bytes);
 
   // Returns true if we are currently loading data.
   bool IsLoading() const;
@@ -136,6 +141,9 @@ class MEDIA_BLINK_EXPORT MultiBufferReader
   int64_t max_buffer_forward_;
   int64_t max_buffer_backward_;
 
+  // The amount of buffer we've added to the global LRU.
+  int64_t current_buffer_size_;
+
   // Currently pinned range.
   Interval<MultiBuffer::BlockId> pinned_range_;