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

media/filters/source_buffer_range.cc

Index: media/filters/source_buffer_range.cc
diff --git a/media/filters/source_buffer_range.cc b/media/filters/source_buffer_range.cc
index a80d629fe8a620d18177e5ecd33aac34811894c9..d78a58422e75a1c6750c5a59a5f82d930f1545e1 100644
--- a/media/filters/source_buffer_range.cc
+++ b/media/filters/source_buffer_range.cc
@@ -316,6 +316,16 @@ int SourceBufferRange::GetRemovalGOP(
   return bytes_removed;
 }
 
+bool SourceBufferRange::FirstGOPEarlierThanMediaTime(
+    DecodeTimestamp media_time) const {
+  if (keyframe_map_.size() == 1u)
+    return (GetEndTimestamp() < media_time);
+
+  KeyframeMap::const_iterator second_gop = keyframe_map_.begin();
+  ++second_gop;
+  return second_gop->first <= media_time;
+}
+
 bool SourceBufferRange::FirstGOPContainsNextBufferPosition() const {
   if (!HasNextBufferPosition())
     return false;