Add about_flag for experimenting MediaSession on Desktop

chrome/app/generated_resources.grd

Index: chrome/app/generated_resources.grd
diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index ce3ce3c822f9dc7ea9eabf0cc35690c5a2d3a9e4..b2d8f0b3bbbad3a5990f46373c605fd7e7a368b1 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -15507,6 +15507,25 @@ read aloud to screenreader users to announce that a completion is available.">
     <message name="IDS_FLAGS_EXPENSIVE_BACKGROUND_TIMER_THROTTLING_DESCRIPTION" desc="Description for the flag to enable expensive background timer throttling">
       Enables intervention to limit CPU usage of background timers to 1%.
     </message>
+
+    <!-- Default MediaSession flag -->

[whywhat, 2016/10/18 17:23:57]

I think from the people who will read this, including translators and users,
only you, me and Mounir will understand what default MediaSession means :)

I think using the text you wrote already instead "managing audio focus across
tabs" would be nicer.

E.g. "Name for the flag to enable managing audio focus across tabs", "Enables
managing audio focus across tabs." etc.
Maybe enable-audio-focus-manager would be a better name for the flag itself.

[Zhiqiang Zhang (Slow), 2016/10/18 18:51:54]

Updated the flag name. I think it's fine for the comment since it's the internal
name.

+    <if expr="not is_android">
+        <message name="IDS_FLAGS_ENABLE_DEFAULT_MEDIA_SESSION_NAME" desc="Name for the flag to enable default MediaSession on desktop">
+            Enable <ph name="FEATURE_NAME">default MediaSession</ph>
+        </message>
+        <message name="IDS_FLAGS_ENABLE_DEFAULT_MEDIA_SESSION_DESCRIPTION" desc="Desciption for the flag to enable default MediaSession on desktop">
+            Enables the default MediaSession for managing audio focus across tabs.
+        </message>
+        <message name="IDS_FLAGS_ENABLE_DEFAULT_MEDIA_SESSION_DISABLED" desc="Option for disabling the default MediaSession">
+            Disabled
+        </message>
+        <message name="IDS_FLAGS_ENABLE_DEFAULT_MEDIA_SESSION_ENABLED" desc="Option for enabling the default MediaSession">
+            Enabled
+        </message>
+        <message name="IDS_FLAGS_ENABLE_DEFAULT_MEDIA_SESSION_ENABLED_WITH_FLASH" desc="Option for enabling the default MediaSession with Flash">
+            Enabled (with Flash)
+        </message>
+    </if>
   </messages>
  </release>
 </grit>