Show Media Router toolbar icon ephemerally for MR dialogs

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

Index: chrome/browser/ui/webui/media_router/media_router_dialog_controller_impl.cc
diff --git a/chrome/browser/ui/webui/media_router/media_router_dialog_controller_impl.cc b/chrome/browser/ui/webui/media_router/media_router_dialog_controller_impl.cc
index de13d04f3e1011061e939c5d3ee6603d15308930..75d4e207e3ca48153e172db95fd5a7a098e51d30 100644
--- a/chrome/browser/ui/webui/media_router/media_router_dialog_controller_impl.cc
+++ b/chrome/browser/ui/webui/media_router/media_router_dialog_controller_impl.cc
@@ -12,6 +12,7 @@
 #include "base/macros.h"
 #include "base/trace_event/trace_event.h"
 #include "build/build_config.h"
+#include "chrome/browser/media/router/media_router_ui_service.h"
 #include "chrome/browser/media/router/presentation_service_delegate_impl.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/browser_finder.h"
@@ -110,6 +111,12 @@ class MediaRouterDialogDelegate : public WebDialogDelegate {
   DISALLOW_COPY_AND_ASSIGN(MediaRouterDialogDelegate);
 };
 
+MediaRouterActionController* GetActionController(WebContents* web_contents) {
+  Profile* profile =
+      Profile::FromBrowserContext(web_contents->GetBrowserContext());
+  return MediaRouterUIService::Get(profile)->action_controller();
+}
+
 }  // namespace
 
 // static
@@ -156,10 +163,13 @@ MediaRouterDialogControllerImpl::MediaRouterDialogControllerImpl(
     WebContents* web_contents)
     : MediaRouterDialogController(web_contents),
       media_router_dialog_pending_(false),
+      action_controller_(GetActionController(web_contents)),
       weak_ptr_factory_(this) {
+  DCHECK(action_controller_);
 }
 
 MediaRouterDialogControllerImpl::~MediaRouterDialogControllerImpl() {
+  Reset();
 }
 
 WebContents* MediaRouterDialogControllerImpl::GetMediaRouterDialog() const {
@@ -262,15 +272,21 @@ void MediaRouterDialogControllerImpl::CreateMediaRouterDialog() {
   dialog_observer_.reset(new DialogWebContentsObserver(
       media_router_dialog, this));
 
+  // The |action_controller_| must be notified after |action_| to avoid a UI

[msw, 2016/11/04 00:07:16]

nit: Maybe override OnDialogShown in the impl to call the action first, then the
base class function? ditto for OnDialogHidden?

[takumif, 2016/11/09 04:37:27]

Sorry, I don't quite understand this comment. (The action controller doesn't
keep track of all the actions, so it can't notify the action.)

[msw, 2016/11/09 20:32:33]

hmm, it's odd that the *dialog* controller tracks the actions, but the *action*
controller doesn't... I guess some of these patterns just aren't obvious to me.

+  // bug in which the drop shadow is drawn in an incorrect position.
   if (action_)
     action_->OnDialogShown();
+  action_controller_->OnDialogShown();
 }
 
 void MediaRouterDialogControllerImpl::Reset() {
+  if (IsShowingMediaRouterDialog()) {

[msw, 2016/11/04 00:07:16]

Is it possible that multiple dialogs are showing when Reset is called, and
OnDialogHidden should be called multiple times to reset the dialog count to 0?

[takumif, 2016/11/09 04:37:27]

Each MediaRouterDialogControllerImpl can have at most one dialog, so if multiple
dialogs are shown, their respective MediaRouterDialogControllerImpls will
together reset the count to 0. 

[msw, 2016/11/09 20:32:34]

Acknowledged.

+    if (action_)
+      action_->OnDialogHidden();
+    action_controller_->OnDialogHidden();
+  }
   MediaRouterDialogController::Reset();
   dialog_observer_.reset();
-  if (action_)
-    action_->OnDialogHidden();
 }
 
 void MediaRouterDialogControllerImpl::OnDialogNavigated(