Cut highdpi resources from builds that don't need it to save space.
Cut highdpi resources from builds that don't need it to save space.

Previously, highdpi was disabled by default, and just enabled on link. This
breaks prebuilts on link because we only have non-highdpi prebuilts.

To fix prebuilts, we enable highdpi by default (including for all developers),
and just disable it in release builds where we care more about how big the
image is. This saves us from needing to build Chrome prebuilts with both highdpi
enabled and disabled.

BUG=chromium-os:33081
TEST=cbuildbot_config_unittest.pyy

Change-Id: Id379b737fd966cfaa774c9422cf1e3bbeb7daefe
Reviewed-on: https://gerrit.chromium.org/gerrit/28726
Reviewed-by: Ryan Cui <5ce1592d53754a87a44fc2eb7b63d5f77cf50fdb@chromium.org>
Commit-Ready: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>
Tested-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>

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