Add CHECK to catch places where BrowserProcessImpl's refcount goes to 0.

base/message_loop.h

Index: base/message_loop.h
diff --git a/base/message_loop.h b/base/message_loop.h
index 732de03aa1f147d2d97477b2223c51b255fd8b47..171bee31ef77872a7dab26d2411fc2fd5221c008 100644
--- a/base/message_loop.h
+++ b/base/message_loop.h
@@ -377,6 +377,9 @@ class BASE_EXPORT MessageLoop : public base::MessagePump::Delegate {
   }
 #endif  // OS_WIN
 
+  // Can only be called from the thread that owns the MessageLoop.
+  bool is_running() const;
+
   //----------------------------------------------------------------------------
  protected:
   struct RunState {