WebController: Set JS Controller after reloading the view

The WebKit delegate method didStartProvisionalLoadForFrame:
is not called when reloading the frame. This caused the
webviews to appear empty.

We fix it by using a delegate method which is called each
reload, as suggested by weinig in #webkit.

This fixes Lighthouse bug #81.

PBWebController.m

@@ -54,7 +54,7 @@
 
 # pragma mark Delegate methods
 
-- (void)webView:(WebView *)sender didStartProvisionalLoadForFrame:(WebFrame *)frame
+- (void)webView:(WebView *)sender didClearWindowObject:(WebScriptObject *)windowObject forFrame:(WebFrame *)frame
 {
 	id script = [view windowScriptObject];
 	[script setValue: self forKey:@"Controller"];

PBWebHistoryController.m

@@ -22,6 +22,7 @@
 
 - (void) didLoad
 {
+	currentSha = @"";
 	[self changeContentTo: historyController.webCommit];
 }