Enable Battery Status API by default in Blink.

Set Battery Status API status to stable in blink. We have
implementations for all platforms supported by blink now,
i.e. on Android, Windows, Linux, ChromeOS and Mac.

BUG=122593
TEST=http://jsbin.com/battery-status-test

Review URL: https://codereview.chromium.org/451583003

git-svn-id: svn://svn.chromium.org/blink/trunk@180296 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/LayoutTests/virtual/stable/webexposed/global-constructors-listing-expected.txt

@@ -30,6 +30,7 @@ AudioParam
 AudioProcessingEvent
 AutocompleteErrorEvent
 BarProp
+BatteryManager
 BeforeUnloadEvent
 BiquadFilterNode
 Blob

third_party/WebKit/Source/platform/RuntimeEnabledFeatures.in

@@ -19,7 +19,7 @@
 ApplicationCache status=stable
 AudioVideoTracks depends_on=Media, status=experimental
 AuthorShadowDOMForAnyElement
-BatteryStatus status=experimental
+BatteryStatus status=stable
 Beacon status=experimental
 
 // This feature is deprecated and we are evangalizing affected sites.