[Android] Enable remote debugging after rebase to M39

Adjust classes according upstream changes of DevToolsManagerDelegate
and DevToolsHttpHandlerDelegate.
Besides, hardcode webkit revision to generate remote frontend url
due to https://code.google.com/p/chromium/issues/detail?id=425912
Thanks for the info. Actually, upstream fix doesn't work for us. The fix make the output of blink devtools resources correct, but we don't use the devtools resources built by our own. So we still need to hardcode the revision here. I've update the revision to the one that lands the specified fix in M39, which is https://codereview.chromium.org/666323002 .
And make the comment more clear when we could revert this hard code.

@sqliu @rakuco .