Improve init-repository.py to fetch up-to-date dependency list

This patch introduces a new mechanism to retrieve submodules.
The utilities in version_resolver.py provide means to download
the upstream DEPS file for a specified Chromium version.
This makes it possible to check out the needed svn branches
and specific revisions used for the release. We still use the
git repositories found in the upstream .DEPS.git file but since
it is not regularly updated after the branch-off, we try to match
the release svn revisions to git shasums which is possible since
each commit includes git-svn-id's.
Also add a maintenance tool get_version.py which reads the Chrome
release information from http://omahaproxy.appspot.com.

We now pin the latest stable channel Chromium release from branch
1650 with the version number 31.0.1650.63 and a branch-off date of
Sept 23rd.

Change-Id: I333ada4250999b442cd244821818bace9e6136f4
Reviewed-by: Zeno Albisser <zeno.albisser@digia.com>
Update chromium patches to apply on current stable (1650)

Change-Id: I3bdad02a2ef69d242980e34774a8219ef0c74ea9
Reviewed-by: Zeno Albisser <zeno.albisser@digia.com>
Fix the QQuickWebEngineView rendering with 1650.

This is now initialized by Chromium in ContentMainRunnerImpl::Run,
which we bypass for our browser process.

Change-Id: Id8233df3fe12048cd2b6eaf870b161ab5d1eb089
Reviewed-by: Andras Becsi <andras.becsi@digia.com>
Reviewed-by: Zeno Albisser <zeno.albisser@digia.com>