Revert of Revert of Make start/stop loading notifications per-frame

public/web/WebFrameClient.h

Index: public/web/WebFrameClient.h
diff --git a/public/web/WebFrameClient.h b/public/web/WebFrameClient.h
index eb49a52886daf2627bb3f0b3fb6996a39fca9028..b218cc86787c5d0cac6fb846b084045b2e9e6947 100644
--- a/public/web/WebFrameClient.h
+++ b/public/web/WebFrameClient.h
@@ -167,6 +167,15 @@
 
     // Navigational notifications ------------------------------------------
 
+    // These notifications bracket any loading that occurs in the WebFrame.
+    virtual void didStartLoading(bool toDifferentDocument) { }
+    virtual void didStopLoading() { }
+
+    // Notification that some progress was made loading the current frame.
+    // loadProgress is a value between 0 (nothing loaded) and 1.0 (frame fully
+    // loaded).
+    virtual void didChangeLoadProgress(double loadProgress) { }
+
     // A form submission has been requested, but the page's submit event handler
     // hasn't yet had a chance to run (and possibly alter/interrupt the submit.)
     virtual void willSendSubmitEvent(WebLocalFrame*, const WebFormElement&) { }