Add a GamepadVibration runtime feature flag

In previous versions, the vibration feature was enabled with the
GamepadExtensions runtime feature flag. This CL splits the vibration
functionality into a separate flag that is enabled by default. This
allows the vibration feature to be enabled independently of other
features that use the same runtime flag.

BUG=749295

Change-Id: Ia8017e8b0ecd9df4490e8b205ecd1f49509c687b
Reviewed-on: https://chromium-review.googlesource.com/1027996
Reviewed-by: Chris Harrelson <[email protected]>
Reviewed-by: Kentaro Hara <[email protected]>
Reviewed-by: Alex Moshchuk <[email protected]>
Commit-Queue: Matt Reynolds <[email protected]>
Cr-Commit-Position: refs/heads/master@{#555211}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 294f03b..9dbf1af 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -505,6 +505,8 @@
 
 extern const char kGamepadExtensionsName[];
 extern const char kGamepadExtensionsDescription[];
+extern const char kGamepadVibrationName[];
+extern const char kGamepadVibrationDescription[];
 
 extern const char kGpuRasterizationMsaaSampleCountName[];
 extern const char kGpuRasterizationMsaaSampleCountDescription[];