Move implementation from header to source.

base/message_loop.h

Index: base/message_loop.h
diff --git a/base/message_loop.h b/base/message_loop.h
index 8deacecd10d293a857ed736809549dee8baa5903..b80fa5a332dcbd4e0b16ae577db689379657c26b 100644
--- a/base/message_loop.h
+++ b/base/message_loop.h
@@ -65,7 +65,7 @@ class MessageLoop : public base::MessagePump::Delegate {
   // NOTE: A TaskObserver implementation should be extremely fast!
   class TaskObserver {
    public:
-    TaskObserver() {}
+    TaskObserver();
 
     // This method is called before processing a task.
     virtual void WillProcessTask(base::TimeTicks birth_time) = 0;
@@ -74,7 +74,7 @@ class MessageLoop : public base::MessagePump::Delegate {
     virtual void DidProcessTask() = 0;
 
    protected:
-    virtual ~TaskObserver() {}
+    virtual ~TaskObserver();
   };
 
   static void EnableHistogrammer(bool enable_histogrammer);
@@ -89,7 +89,7 @@ class MessageLoop : public base::MessagePump::Delegate {
   //
   class DestructionObserver {
    public:
-    virtual ~DestructionObserver() {}
+    virtual ~DestructionObserver();
     virtual void WillDestroyCurrentMessageLoop() = 0;
   };