Add a patcher script to apply patches

1. Patcher is a helper to apply patches to certain repos.
2. It runs in hooks of DEPS after fetching deps successfully.
3. patch.cfg is used to config the patch path and target repo path.
4. These python scripts origin from CEF project.
Merge pull request #1051 from xingnan/patcher

Add a patcher script to apply patches
[Android] Add thread safety checking for XWalkView.

All XWalkView methods must be called on the UI thread.
Throw an exception when XWalkView methods are called from
other thread. So all unit test cases need to be refined for
this change.

BUG=https://crosswalk-project.org/jira/browse/XWALK-98