A separate feature flag for ALS and Magnetometer

This CL introduces the "GenericSensorExtraClasses" feature flag
for sensor classes which expose previously unavailable
platform features (i.e ALS, Magnetometer).

Thus, the existing "GenericSensor" feature flag can be used
to expose only a restricted set of motion sensor classes which
are replacements for the DeviceMotionEvent and DeviceOrientationEvent
interfaces.

Bug: 750018
Change-Id: I31093784fb92fd7eb33de140de1cdb2acb4773f8
Reviewed-on: https://chromium-review.googlesource.com/623716
Reviewed-by: Kentaro Hara <[email protected]>
Reviewed-by: Jochen Eisinger <[email protected]>
Reviewed-by: Reilly Grant <[email protected]>
Commit-Queue: Mikhail Pozdnyakov <[email protected]>
Cr-Commit-Position: refs/heads/master@{#497108}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 817a066..f306bb5 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -222,6 +222,9 @@
 extern const char kEnableGenericSensorName[];
 extern const char kEnableGenericSensorDescription[];
 
+extern const char kEnableGenericSensorExtraClassesName[];
+extern const char kEnableGenericSensorExtraClassesDescription[];
+
 extern const char kEnableHDRName[];
 extern const char kEnableHDRDescription[];