Add chrome.power extension API.

This moves the chrome.experimental.power API to
chrome.power, makes minor changes to its public interface
(adding a "level" parameter to requestKeepAwake() and
removing the callbacks from both methods), adds unit tests
for it, and adds a sample "Keep Awake" extension meant to
replace the existing Chrome OS-specific extension at
http://goo.gl/CrUzi.

BUG=178944
[email protected]

Review URL: https://chromiumcodereview.appspot.com/12576018

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@189253 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/browser/extensions/extension_function_histogram_value.h b/chrome/browser/extensions/extension_function_histogram_value.h
index ab247a306..c2cb528 100644
--- a/chrome/browser/extensions/extension_function_histogram_value.h
+++ b/chrome/browser/extensions/extension_function_histogram_value.h
@@ -492,6 +492,8 @@
   SYNCFILESYSTEM_GETCONFLICTRESOLUTIONPOLICY,
   NETWORKINGPRIVATE_SETPROPERTIES,
   NETWORKINGPRIVATE_GETSTATE,
+  POWER_REQUESTKEEPAWAKE,
+  POWER_RELEASEKEEPAWAKE,
   ENUM_BOUNDARY // Last entry: Add new entries above.
 };