Read got_revision_mapping from built in spec
Read got_revision_mapping from built in spec

Sometimes the spec passed in via parameters also have got_revision_mapping that
we want to use.

BUG=590788

Review URL: https://codereview.chromium.org/1748143002

git-svn-id: fd409f4bdeea2bb50a5d34bb4d4bfc2046a5a3dd@299015 0039d316-1c4b-4281-b951-d872f2087c98

primiano/depot_tools,CoherentLabs/depot_tools,CoherentLabs/depot_tools,primiano/depot_tools,primiano/depot_tools