[DeviceLight] Add Layout support

content/public/test/layouttest_support.h

Index: content/public/test/layouttest_support.h
diff --git a/content/public/test/layouttest_support.h b/content/public/test/layouttest_support.h
index 7bb8e89074e01637df07624ebe351412dfd30a96..bf30db5a9ad88727308d802e6bac1fe8a49bf42f 100644
--- a/content/public/test/layouttest_support.h
+++ b/content/public/test/layouttest_support.h
@@ -48,6 +48,10 @@ void EnableWebTestProxyCreation(
 // Sets gamepad provider to be used for layout tests.
 void SetMockGamepadProvider(RendererGamepadProvider* provider);
 
+// Sets a double that should be used when registering
+// a listener through WebKitPlatformSupport::setDeviceLightListener().
+void SetMockDeviceLightData(const double data);
+
 // Sets WebDeviceMotionData that should be used when registering
 // a listener through WebKitPlatformSupport::setDeviceMotionListener().
 void SetMockDeviceMotionData(const blink::WebDeviceMotionData& data);