Convert ebuild to pull chrome sources from git.

Re-landing this:

https://chromium-review.googlesource.com/212790

It should work now, after this change to gclient:

https://codereview.chromium.org/490233003

... and after rolling that change into the manifest:

https://chromium-review.googlesource.com/#/c/213524/
https://chrome-internal-review.googlesource.com/#/c/173395/

BUG=chromium:376027
TEST=scripts/cros_mark_chrome_as_stable_unittest.py

Change-Id: I20c2a6d3a221fae0a3849628b688cded996834b4
Reviewed-on: https://chromium-review.googlesource.com/213460
Reviewed-by: David James <davidjames@chromium.org>
Tested-by: Stefan Zager <szager@chromium.org>
diff --git a/scripts/sync_chrome.py b/scripts/sync_chrome.py
index bddea2d..a090fc0 100644
--- a/scripts/sync_chrome.py
+++ b/scripts/sync_chrome.py
@@ -19,8 +19,8 @@
   version = parser.add_mutually_exclusive_group()
   version.add_argument('--tag', help='Sync to specified Chrome release',
                        dest='version')
-  version.add_argument('--revision', help='Sync to specified SVN revision',
-                       type=int, dest='version')
+  version.add_argument('--revision', help='Sync to specified git revision',
+                       dest='version')
 
   parser.add_argument('--internal', help='Sync internal version of Chrome',
                       action='store_true', default=False)