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

media/blink/websourcebuffer_impl.cc

Index: media/blink/websourcebuffer_impl.cc
diff --git a/media/blink/websourcebuffer_impl.cc b/media/blink/websourcebuffer_impl.cc
index 3491378f2d9f988c6ade4735638ef47b33fcacef..c20c9415bec6c78588de908e0a52b3ec21f0dca2 100644
--- a/media/blink/websourcebuffer_impl.cc
+++ b/media/blink/websourcebuffer_impl.cc
@@ -81,6 +81,10 @@ blink::WebTimeRanges WebSourceBufferImpl::buffered() {
   return result;
 }
 
+bool WebSourceBufferImpl::evictCodedFrames() {
+  return demuxer_->EvictFrames();
+}
+
 void WebSourceBufferImpl::append(
     const unsigned char* data,
     unsigned length,