Merge jquery.placeholder with github.com/mathiasbynens/jquery-placeholder

This is a fork from Mathias Bynens' jquery.placeholder as of this commit
https://github.com/mathiasbynens/jquery-placeholder/blob/47f05d400e2dd16b59d144141a2cf54a9a77c502/jquery.placeholder.js

New features added:
* Support for valHooks and propHooks
* Clearing placeholders upon for submission
* jquery.placeholder QUnit test suite

Bug: 57179
Change-Id: I1ecca3d89bb964414ad8765caaa7e1958b94f762
Merge "Merge jquery.placeholder with github.com/mathiasbynens/jquery-placeholder"