Add mojom for WindowOpenDisposition

Adds ui::mojom::WindowOpenDisposition and a typemap which maps it
to ::WindowOpenDisposition. This will be useful when converting
existing IPCs to mojom.

C++ references to WindowOpenDisposition are left alone for now and
we'll rely on the typemap to do its thing for Mojo messages.

Java references have been updated to use the mojom generated type
directly, removing window_open_disposition.h from the set of headers
processed by a java_cpp_enum rule.

BUG=612500

Review-Url: https://codereview.chromium.org/2363533002
Cr-Commit-Position: refs/heads/master@{#420211}
17 files changed