Add global-media-controls-for-cast to chrome://flags

Add a flag to show Cast sessions in the Global Media Controls UI.

Bug: 987479
Change-Id: Iaeb93ec79365319020bde0c216091a861d8de509
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1971050
Reviewed-by: Tommy Steimel <[email protected]>
Commit-Queue: Takumi Fujimoto <[email protected]>
Cr-Commit-Position: refs/heads/master@{#726173}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 79d560f..3a5b47b 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -671,6 +671,9 @@
 extern const char kGlobalMediaControlsName[];
 extern const char kGlobalMediaControlsDescription[];
 
+extern const char kGlobalMediaControlsForCastName[];
+extern const char kGlobalMediaControlsForCastDescription[];
+
 extern const char kGpuRasterizationName[];
 extern const char kGpuRasterizationDescription[];
 extern const char kForceGpuRasterization[];