[Media Router] Make per-hostname cast mode selections persist

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

Index: chrome/browser/ui/webui/media_router/media_router_webui_message_handler.cc
diff --git a/chrome/browser/ui/webui/media_router/media_router_webui_message_handler.cc b/chrome/browser/ui/webui/media_router/media_router_webui_message_handler.cc
index 6fe551cc3eb3bdf03ab5155bee361996b704caef..e9bfe75834b71f016b7610294556181ca351dbe4 100644
--- a/chrome/browser/ui/webui/media_router/media_router_webui_message_handler.cc
+++ b/chrome/browser/ui/webui/media_router/media_router_webui_message_handler.cc
@@ -419,6 +419,14 @@ void MediaRouterWebUIMessageHandler::OnRequestInitialData(
       cast_modes, media_router_ui_->GetPresentationRequestSourceName()));
   initial_data.Set("castModes", cast_modes_list.release());
 
+  MediaCastMode initial_cast_mode =

[imcheng, 2016/11/14 19:56:59]

What if |initial_cast_mode| is not in |cast_modes|?

[takumif, 2016/11/16 01:34:27]

Checking to make sure TAB_MIRROR is in |cast_modes| when overriding with tab
mirroring.

+      media_router_ui_->GetCastModeSelectionForCurrentHost();
+  if (initial_cast_mode != MediaCastMode::DEFAULT) {

[takumif, 2016/11/08 22:52:16]

Right now, GetCastModeSelectionForCurrentHost() returns MediaCastMode::DEFAULT
if user hasn't chosen anything, so we can't distinguish between sites where the
user has chosen DEFAULT and hasn't chosen anything. So in the case the user has
chosen DEFAULT we don't set the initial cast mode, but the webui defaults to
DEFAULT anyways.

I thought about making GetCastModeSelectionForCurrentHost() return an int
(instead of MediaCastMode) and make it return 0 to indicate the user hasn't
chosen anything, but that didn't seem as clean. apacible@, I wonder if the
current way is okay, or there's a better way to do this.

[apacible, 2016/11/11 22:40:23]

This looks fine.

[takumif, 2016/11/12 00:08:31]

Okay!

[imcheng, 2016/11/14 19:56:59]

Saw this comment after I posted my own comments. Note there is a slight
difference in behavior if we don't set initialCastMode = DEFAULT.
- if initialCastMode is not set, the dialog is in AUTO mode - which means we
will show sinks that are compatible with any one cast mode, and we will create
route using the best cast mode (DEFAULT > TAB_MIRROR > DESKTOP_MIRROR) when
selected.
- if set, the dialog will only show devices that can do DEFAULT mode.


The code here effectively means we are only setting initialCastMode for
TAB_MIRROR only, or not at all. Do we plan to support initialCastMode = DEFAULT?
(It doesn't look very useful to me, under the assumption that DEFAULT >
TAB_MIRROR). If not, would it suffice to just store a boolean instead of int as
the pref?

Finally, please document the logic here and any assumptions made regarding the
use of DEFAULT. 

[takumif, 2016/11/16 01:34:27]

Changing the pref to only keep track of hostnames set to TAB_MIRROR.

+    initial_data.Set(
+        "initialCastMode",
+        new base::FundamentalValue(static_cast<int>(initial_cast_mode)));
+  }
+
   web_ui()->CallJavascriptFunctionUnsafe(kSetInitialData, initial_data);
   media_router_ui_->UIInitialized();
 }
@@ -698,6 +706,8 @@ void MediaRouterWebUIMessageHandler::OnReportSelectedCastMode(
   }
   UMA_HISTOGRAM_SPARSE_SLOWLY("MediaRouter.Ui.Navigate.SourceSelection",
                               cast_mode_type);
+  media_router_ui_->RecordCastModeSelection(
+      static_cast<MediaCastMode>(cast_mode_type));
 }
 
 void MediaRouterWebUIMessageHandler::OnReportSinkCount(