[Media Router] Implement MediaRouterAction + MediaRouterUI tests.

chrome/browser/ui/webui/media_router/media_router_dialog_controller.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/webui/media_router/media_router_dialog_controller.h"
 
 #include <string>
 #include <vector>
 
 #include "chrome/browser/profiles/profile.h"
@@ skipping 82 matching lines @@
 #if defined(OS_MACOSX)
   *size = gfx::Size(330, 400);
 #else
   // size is not used because the dialog is auto-resizeable.
   *size = gfx::Size();
 #endif
 }
 
 }  // namespace
 
+// static
+MediaRouterDialogController*
+MediaRouterDialogController::GetOrCreateForWebContents(
+    WebContents* web_contents) {
+  DCHECK(web_contents);
+  MediaRouterDialogController* controller =
+      media_router::MediaRouterDialogController::FromWebContents(web_contents);

[Peter Kasting, 2015/06/04 00:17:53]

Nit: media_router:: namespace qualifier not necessary (and you don't use it
below)

[imcheng (use chromium acct), 2015/06/04 01:04:20]

Done.

+  if (controller)
+    return controller;
+
+  MediaRouterDialogController::CreateForWebContents(web_contents);
+  controller = MediaRouterDialogController::FromWebContents(web_contents);
+  DCHECK(controller);
+  return controller;

[Peter Kasting, 2015/06/04 00:17:53]

Nit: This function is more verbose than it needs to be, because
CreateForWebContents() will automatically no-op if the object exists.  So just
something like:

{
  // This call does nothing if the controller already exists.
  MediaRouterDialogController::CreateForWebContents(web_contents);
  return MediaRouterDialogController::FromWebContents(web_contents);
}

[imcheng (use chromium acct), 2015/06/04 01:04:20]

My reasoning was that although CreateForWebContents is no-op when called a
second time, it still has to check for the existence for the
MediaRouterDialogController in order for it to no-op. It's also an extra
function call. But I guess it does not make a big difference in terms of
performance, so I took your suggestion.

+}
+
 class MediaRouterDialogController::DialogWebContentsObserver
     : public content::WebContentsObserver {
  public:
   DialogWebContentsObserver(
       WebContents* web_contents,
       MediaRouterDialogController* dialog_controller)
       : content::WebContentsObserver(web_contents),
         dialog_controller_(dialog_controller) {
   }
 
@@ skipping 159 matching lines @@
       << "transition_type: " << transition_type << ", "
       << "nav_type: " << nav_type;
 
   media_router_dialog_pending_ = false;
 
   // TODO(imcheng): Initialize dialog.
 }
 
 }  // namespace media_router