Add the ability to observe MessagePumpMojo

mojo/common/message_pump_mojo.h

Index: mojo/common/message_pump_mojo.h
diff --git a/mojo/common/message_pump_mojo.h b/mojo/common/message_pump_mojo.h
index 26e28b1067a20639bc5b9fc79f137da54d29b260..4dd715568800bf961a0a60cc9cecbd8cdb331f7f 100644
--- a/mojo/common/message_pump_mojo.h
+++ b/mojo/common/message_pump_mojo.h
@@ -10,6 +10,7 @@
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop/message_pump.h"
+#include "base/observer_list.h"
 #include "base/synchronization/lock.h"
 #include "base/time/time.h"
 #include "mojo/common/mojo_common_export.h"
@@ -23,6 +24,17 @@ class MessagePumpMojoHandler;
 // Mojo implementation of MessagePump.
 class MOJO_COMMON_EXPORT MessagePumpMojo : public base::MessagePump {
  public:
+  class Observer {
+   public:
+    Observer() {}
+
+    virtual void WillSignalHandler() = 0;
+    virtual void DidSignalHandler() = 0;
+
+   protected:
+    virtual ~Observer() {}
+  };
+
   MessagePumpMojo();
   virtual ~MessagePumpMojo();
 
@@ -45,6 +57,9 @@ class MOJO_COMMON_EXPORT MessagePumpMojo : public base::MessagePump {
 
   void RemoveHandler(const Handle& handle);
 
+  void AddObserver(Observer*);
+  void RemoveObserver(Observer*);
+
   // MessagePump:
   virtual void Run(Delegate* delegate) override;
   virtual void Quit() override;
@@ -88,6 +103,9 @@ class MOJO_COMMON_EXPORT MessagePumpMojo : public base::MessagePump {
   // Returns the deadline for the call to MojoWaitMany().
   MojoDeadline GetDeadlineForWait(const RunState& run_state) const;
 
+  void WillSignalHandler();
+  void DidSignalHandler();
+
   // If non-NULL we're running (inside Run()). Member is reference to value on
   // stack.
   RunState* run_state_;
@@ -106,6 +124,8 @@ class MOJO_COMMON_EXPORT MessagePumpMojo : public base::MessagePump {
   // notify it.
   int next_handler_id_;
 
+  ObserverList<Observer> observers_;
+
   DISALLOW_COPY_AND_ASSIGN(MessagePumpMojo);
 };