[Alarm] Fix failures raised from test suite.

I've downloaded the test suite from http://otcqa.sh.intel.com/qa-auto/live/Web_TCT_Xwalk/ and run them manually.
All the alarm related failures in the test suite have been fixed.

BUG=XWALK-2163
Ah, interesting result. I doubt this operation is not so hot that require our code to do such kind of optimization. Anway, I'm okay with this change. thanks for the link. I'll merge it when lgtm from @deqing