Ignore chromium repos when calculating diffs
Ignore chromium repos when calculating diffs

Try 2. We should ignore all chromium code changes when calculating
ChromeOS manifest differences.

BUG=chromium-os:25389
TEST=run_tests in chromite/buildbot (all pass except
     cros_mark_chrome_as_stable_unittest, fails for unrelated reason)

Change-Id: I2a5db00b8c23b45b7a41ceb443a20eaea2969b3e
Reviewed-on: https://gerrit.chromium.org/gerrit/15854
Reviewed-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>
Commit-Ready: Eric Blake <a9da18479c871fe903d9590822cfe2629c6a4d11@chromium.org>
Tested-by: Eric Blake <a9da18479c871fe903d9590822cfe2629c6a4d11@chromium.org>

chadversary/chromiumos.chromite,coreos/chromite,chadversary/chromiumos.chromite,zhang0137/chromite,zhang0137/chromite,bpsinc-native/src_third_party_chromite,zhang0137/chromite,coreos/chromite,coreos/chromite,bpsinc-native/src_third_party_chromite,bpsinc-native/src_third_party_chromite