[Display Cutout] Add feature for media controls

Add a feature for media controls to recognise a gesture
and expand into the display cutout.

BUG=849790

Change-Id: Ice6de82f4fb94e366fca68338a55236fa1f05c8a
Reviewed-on: https://chromium-review.googlesource.com/1087710
Reviewed-by: Jochen Eisinger <[email protected]>
Commit-Queue: Becca Hughes <[email protected]>
Cr-Commit-Position: refs/heads/master@{#568142}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 995f691..7ad19b5 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1308,6 +1308,9 @@
 extern const char kEnableDataReductionProxyMainMenuName[];
 extern const char kEnableDataReductionProxyMainMenuDescription[];
 
+extern const char kEnableMediaControlsExpandGestureName[];
+extern const char kEnableMediaControlsExpandGestureDescription[];
+
 extern const char kEnableOmniboxClipboardProviderName[];
 extern const char kEnableOmniboxClipboardProviderDescription[];