Makes mojo WebUI run main only after page finishes loading

content/renderer/web_ui_mojo.cc

Index: content/renderer/web_ui_mojo.cc
diff --git a/content/renderer/web_ui_mojo.cc b/content/renderer/web_ui_mojo.cc
index 21d85dacaa867df80c28f236c7732b3006a4ee0b..58f67a85b1f8a05bea8765b447bad967b53fd9ee 100644
--- a/content/renderer/web_ui_mojo.cc
+++ b/content/renderer/web_ui_mojo.cc
@@ -41,18 +41,23 @@ void WebUIMojo::MainFrameObserver::WillReleaseScriptContext(
   web_ui_mojo_->DestroyContextState(context);
 }
 
+void WebUIMojo::MainFrameObserver::DidFinishDocumentLoad() {
+  web_ui_mojo_->OnDidFinishDocumentLoad();
+}
+
 WebUIMojo::WebUIMojo(RenderView* render_view)
     : RenderViewObserver(render_view),
       RenderViewObserverTracker<WebUIMojo>(render_view),
-      main_frame_observer_(this) {
+      main_frame_observer_(this),
+      did_finish_document_load_(false) {
   CreateContextState();
 }
 
 void WebUIMojo::SetBrowserHandle(mojo::ScopedMessagePipeHandle handle) {
-  v8::HandleScope handle_scope(blink::mainThreadIsolate());
-  WebUIMojoContextState* state = GetContextState();
-  if (state)
-    state->SetHandle(handle.Pass());
+  if (did_finish_document_load_)
+    SetHandleOnContextState(handle.Pass());
+  else
+    pending_handle_ = handle.Pass();
 }
 
 WebUIMojo::~WebUIMojo() {
@@ -76,6 +81,20 @@ void WebUIMojo::DestroyContextState(v8::Handle<v8::Context> context) {
   context_data->RemoveUserData(kWebUIMojoContextStateKey);
 }
 
+void WebUIMojo::OnDidFinishDocumentLoad() {
+  did_finish_document_load_ = true;
+  if (pending_handle_.is_valid())
+    SetHandleOnContextState(pending_handle_.Pass());
+}
+
+void WebUIMojo::SetHandleOnContextState(mojo::ScopedMessagePipeHandle handle) {
+  DCHECK(did_finish_document_load_);
+  v8::HandleScope handle_scope(blink::mainThreadIsolate());
+  WebUIMojoContextState* state = GetContextState();
+  if (state)
+    state->SetHandle(handle.Pass());
+}
+
 WebUIMojoContextState* WebUIMojo::GetContextState() {
   blink::WebFrame* frame = render_view()->GetWebView()->mainFrame();
   v8::HandleScope handle_scope(blink::mainThreadIsolate());