Work in progress: Adds MessagePumpDispatcher::ShouldExit(). This is used to handle the

base/message_pump_dispatcher.h

Index: base/message_pump_dispatcher.h
diff --git a/base/message_pump_dispatcher.h b/base/message_pump_dispatcher.h
index 685e92be7d8ee7c8708341363a2ef5c0736181fd..d9860c05e393a01890e401af85c49ce6491a946f 100644
--- a/base/message_pump_dispatcher.h
+++ b/base/message_pump_dispatcher.h
@@ -15,11 +15,12 @@ namespace base {
 // events when |MessageLoop::RunWithDispatcher| is invoked.  If
 // |MessageLoop::Run| is invoked, MessageLoop does not dispatch events
 // (or invoke TranslateMessage), rather every message is passed to
-// Dispatcher's Dispatch method for dispatch. It is up to the
-// Dispatcher whether or not to dispatch the event.
+// Dispatcher's Dispatch() method for dispatch. It is up to the
+// Dispatcher whether or not to dispatch the event. Additionally, before
+// any Tasks are processed ShouldExit() is invoked.
 //
-// The nested loop is exited by either posting a quit, or returning false
-// from Dispatch.
+// The nested loop is exited by either posting a quit, or returning false from
+// Dispatch() or ShouldExit().
 class BASE_EXPORT MessagePumpDispatcher {
  public:
   virtual ~MessagePumpDispatcher() {}
@@ -27,6 +28,10 @@ class BASE_EXPORT MessagePumpDispatcher {
   // Dispatches the event. If true is returned processing continues as
   // normal. If false is returned, the nested loop exits immediately.
   virtual bool Dispatch(const NativeEvent& event) = 0;
+
+  // Returns true if the loop should exit before processing a task.
+  // NOTE: this is currently only wired up on Linux.
+  virtual bool ShouldExit() = 0;
 };
 
 }  // namespace base