git: make fetch chromium use unmanaged mode

This has been determined to work in a better,
more predictable and robust way.

BUG=none
R=szager@google.com

Review URL: https://codereview.chromium.org/22852017

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@219121 0039d316-1c4b-4281-b951-d872f2087c98

recipes/chromium.py

@@ -18,7 +18,7 @@ class Chromium(recipe_util.Recipe):
     solution = { 'name'   :'src',
                  'url'    : url,
                  'deps_file': '.DEPS.git',
-                 'managed'   : True,
+                 'managed'   : False,
                  'custom_deps': {},
                  'safesync_url': '',
     }