Fix audio glitch when audio stream first starts up.

content/browser/renderer_host/media/audio_sync_reader.cc

Index: content/browser/renderer_host/media/audio_sync_reader.cc
===================================================================
--- content/browser/renderer_host/media/audio_sync_reader.cc	(revision 98490)
+++ content/browser/renderer_host/media/audio_sync_reader.cc	(working copy)
@@ -33,6 +33,10 @@
   // Get the data from the buffer.
   memcpy(data, shared_memory_->memory(), read_size);
 
+  // If amount read was less than requested, then zero out the remainder.
+  if (read_size < size)
+    memset(static_cast<char*>(data) + read_size, 0, size - read_size);
+
   // Zero out the entire buffer.
   memset(shared_memory_->memory(), 0, max_size);