Allow MessageFilters to restrict listening to specific message classes

ipc/ipc_channel_proxy.h

Index: ipc/ipc_channel_proxy.h
diff --git a/ipc/ipc_channel_proxy.h b/ipc/ipc_channel_proxy.h
index 1f5ecf450df7f7c6d8a486a3d4efb76a95e1f81e..b326b6740fae4589ebb4dd7e70e4a7874a82ec24 100644
--- a/ipc/ipc_channel_proxy.h
+++ b/ipc/ipc_channel_proxy.h
@@ -14,6 +14,7 @@
 #include "ipc/ipc_channel.h"
 #include "ipc/ipc_channel_handle.h"
 #include "ipc/ipc_listener.h"
+#include "ipc/ipc_message_start.h"
 #include "ipc/ipc_sender.h"
 
 namespace base {
@@ -88,6 +89,13 @@ class IPC_EXPORT ChannelProxy : public Sender, public base::NonThreadSafe {
     // the message be handled in the default way.
     virtual bool OnMessageReceived(const Message& message);
 
+    // Called to query the Message classes supported by the filter.  Return
+    // false to indicate that all message types should reach the filter, or true
+    // if the resulting contents of |supported_message_classes| may be used to
+    // selectively offer messages of a particular class to the filter.
+    virtual bool GetSupportedMessageClasses(
+        std::vector<uint32>* supported_message_classes) const;
+
    protected:
     virtual ~MessageFilter();
 
@@ -224,12 +232,22 @@ class IPC_EXPORT ChannelProxy : public Sender, public base::NonThreadSafe {
     Listener* listener_;
 
     // List of filters.  This is only accessed on the IPC thread.
-    std::vector<scoped_refptr<MessageFilter> > filters_;
+    std::vector<scoped_refptr<MessageFilter> > all_filters_;
     scoped_refptr<base::SingleThreadTaskRunner> ipc_task_runner_;
     scoped_ptr<Channel> channel_;
     std::string channel_id_;
     bool channel_connected_called_;
 
+    // List of global and selective filters; a given filter from |all_filters_|
+    // will exists in either |message_global_filters_| OR
+    // |message_class_filters_|, but not both.
+    // Note that |message_global_filters_| will be given first offering of any
+    // given message.  It's the filter implementer and installer's
+    // responsibility to ensure that a filter is either global or selective to
+    // ensure proper message filtering order.
+    std::vector<MessageFilter*> message_global_filters_;
+    std::vector<MessageFilter*> message_class_filters_[LastIPCMsgStart];
+
     // Holds filters between the AddFilter call on the listerner thread and the
     // IPC thread when they're added to filters_.
     std::vector<scoped_refptr<MessageFilter> > pending_filters_;