Allow MessageFilters to restrict listening to specific message classes

content/browser/renderer_host/media/midi_host.cc

Index: content/browser/renderer_host/media/midi_host.cc
diff --git a/content/browser/renderer_host/media/midi_host.cc b/content/browser/renderer_host/media/midi_host.cc
index b6e26886db7902bbd0071a9bea3f86cc0f387b00..c1f9f63a84f2e75d4741df36f2b778bba02a41bf 100644
--- a/content/browser/renderer_host/media/midi_host.cc
+++ b/content/browser/renderer_host/media/midi_host.cc
@@ -35,6 +35,10 @@ const size_t kMaxInFlightBytes = 10 * 1024 * 1024;  // 10 MB.
 // how many bytes will be sent before reporting back to the renderer.
 const size_t kAcknowledgementThresholdBytes = 1024 * 1024;  // 1 MB.
 
+const uint32 kFilteredMessageClasses[] = {
+  MidiMsgStart,
+};
+
 bool IsDataByte(uint8 data) {
   return (data & 0x80) == 0;
 }
@@ -49,7 +53,9 @@ using media::kSysExByte;
 using media::kEndOfSysExByte;
 
 MidiHost::MidiHost(int renderer_process_id, media::MidiManager* midi_manager)
-    : renderer_process_id_(renderer_process_id),
+    : BrowserMessageFilter(
+          kFilteredMessageClasses, arraysize(kFilteredMessageClasses)),
+      renderer_process_id_(renderer_process_id),
       has_sys_ex_permission_(false),
       midi_manager_(midi_manager),
       sent_bytes_in_flight_(0),