Reapply 169371 "DevTools: defer styles delta calculation to until the end of the task"

Source/core/inspector/InspectorController.h

Index: Source/core/inspector/InspectorController.h
diff --git a/Source/core/inspector/InspectorController.h b/Source/core/inspector/InspectorController.h
index 701e88309cd3177e92542eb9af5b4f267f9335cb..0c85ea5472508f4ad187a785ff736c9411cfed59 100644
--- a/Source/core/inspector/InspectorController.h
+++ b/Source/core/inspector/InspectorController.h
@@ -121,6 +121,7 @@ public:
 
     void willProcessTask();
     void didProcessTask();
+    void flushPendingFrontendMessages();
 
     void didCommitLoadForMainFrame();
     void didBeginFrame(int frameId);
@@ -134,6 +135,7 @@ public:
 
     void willAddPageOverlay(const GraphicsLayer*);
     void didRemovePageOverlay(const GraphicsLayer*);
+
 private:
     InspectorController(Page*, InspectorClient*);