[Global Media Controls] Add HardwareMediaKeyHandling to about flags

Bug: 902792
Change-Id: I8341a1cfd4a4c0046e35d0dd37b1e0742d92fd51
Reviewed-on: https://chromium-review.googlesource.com/c/1418398
Reviewed-by: Avi Drissman <[email protected]>
Reviewed-by: Becca Hughes <[email protected]>
Commit-Queue: Tommy Steimel <[email protected]>
Cr-Commit-Position: refs/heads/master@{#624239}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index a4493f9..9367cd79 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -661,6 +661,9 @@
 extern const char kHandwritingGestureName[];
 extern const char kHandwritingGestureDescription[];
 
+extern const char kHardwareMediaKeyHandling[];
+extern const char kHardwareMediaKeyHandlingDescription[];
+
 extern const char kHarfbuzzRendertextName[];
 extern const char kHarfbuzzRendertextDescription[];