Allow MessageFilters to restrict listening to specific message classes

content/public/browser/browser_message_filter.cc

Index: content/public/browser/browser_message_filter.cc
diff --git a/content/public/browser/browser_message_filter.cc b/content/public/browser/browser_message_filter.cc
index e72a484d9687cb8019d529494bc659573c451ace..72b4a1cfc3d83e5a2f509f6ea311c9b47c049215 100644
--- a/content/public/browser/browser_message_filter.cc
+++ b/content/public/browser/browser_message_filter.cc
@@ -76,6 +76,14 @@ class BrowserMessageFilter::Internal : public IPC::ChannelProxy::MessageFilter {
     return true;
   }
 
+  virtual bool GetSupportedMessageClasses(
+      std::vector<uint32>* supported_message_classes) const OVERRIDE {
+    supported_message_classes->assign(
+        filter_->message_classes_to_filter().begin(),
+        filter_->message_classes_to_filter().end());
+    return true;
+  }
+
   // Dispatches a message to the derived class.
   bool DispatchMessage(const IPC::Message& message) {
     bool message_was_ok = true;
@@ -96,12 +104,28 @@ class BrowserMessageFilter::Internal : public IPC::ChannelProxy::MessageFilter {
   DISALLOW_COPY_AND_ASSIGN(Internal);
 };
 
-BrowserMessageFilter::BrowserMessageFilter()
-    : internal_(NULL), channel_(NULL),
+BrowserMessageFilter::BrowserMessageFilter(uint32 message_class_to_filter)
+    : internal_(NULL),
+      channel_(NULL),
+#if defined(OS_WIN)
+      peer_handle_(base::kNullProcessHandle),
+#endif
+      peer_pid_(base::kNullProcessId),
+      message_classes_to_filter_(1, message_class_to_filter) {}
+
+BrowserMessageFilter::BrowserMessageFilter(
+    const uint32* message_classes_to_filter,
+    size_t num_message_classes_to_filter)
+    : internal_(NULL),
+      channel_(NULL),
 #if defined(OS_WIN)
       peer_handle_(base::kNullProcessHandle),
 #endif
-      peer_pid_(base::kNullProcessId) {
+      peer_pid_(base::kNullProcessId),
+      message_classes_to_filter_(
+          message_classes_to_filter,
+          message_classes_to_filter + num_message_classes_to_filter) {
+  DCHECK(num_message_classes_to_filter);
 }
 
 base::ProcessHandle BrowserMessageFilter::PeerHandle() {