Reviewed by Eric Seidel.

        Add webkit-patch roll-chromium-deps
        https://bugs.webkit.org/show_bug.cgi?id=53288

        This command updates the Source/WebKit/chromium/DEPS file with the
        last-known good revision of Chromium (or a revision specified on the
        command line).  I'd eventually like to turn this into a SheriffBot
        command, but this is the first step.

        This patch somewhat sprawled because I needed to move a bunch of code
        out of ChangeLog that should never have been there in the first place.
        Also, I had to fix a bug in MockUser in order to test the new command.

        * Scripts/webkitpy/common/checkout/api.py:
        * Scripts/webkitpy/common/checkout/changelog.py:
        * Scripts/webkitpy/common/checkout/changelog_unittest.py:
        * Scripts/webkitpy/common/checkout/deps.py: Added.
        * Scripts/webkitpy/common/config/urls.py:
        * Scripts/webkitpy/tool/commands/__init__.py:
        * Scripts/webkitpy/tool/commands/download_unittest.py:
        * Scripts/webkitpy/tool/commands/roll.py: Added.
        * Scripts/webkitpy/tool/commands/roll_unittest.py: Added.
        * Scripts/webkitpy/tool/commands/upload_unittest.py:
        * Scripts/webkitpy/tool/mocktool.py:
        * Scripts/webkitpy/tool/steps/__init__.py:
        * Scripts/webkitpy/tool/steps/preparechangelogfordepsroll.py: Added.
        * Scripts/webkitpy/tool/steps/preparechangelogforrevert.py:
        * Scripts/webkitpy/tool/steps/preparechangelogforrevert_unittest.py: Added.
        * Scripts/webkitpy/tool/steps/suggestreviewers_unittest.py:
        * Scripts/webkitpy/tool/steps/updatechromiumdeps.py: Added.
        * Scripts/webkitpy/tool/steps/validatechangelogs_unittest.py:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@76926 268f45cc-cd09-0410-ab3c-d52691b4dbfc