Move ViewHostMsg_CreateWindow to mojom

Converts this message, addressing several of its dependencies
in the process:

 - Makes content::WindowContainerType an alias for the new
   content::mojom::WindowContainerType. Some transitional public
   constants have been added to satisfy existing references to
   the old enum values. This will be removed in future CLs.
 - Adds a mojom definition for blink::mojom::WindowFeatures,
   corresponding to blink::WebWindowFeatures. A typemap is
   added between these types and is shared by both Blink and
   Chromium bindings configurations.
 - Adds a blink::mojom::Referrer struct analogous to
   content::Renderer. Chromium bindings typemap this new mojom
   struct to content::Referrer.
 - Adds a mojom blink::mojom::ReferrerPolicy enum with a typemap
   to blink::WebReferrerPolicy, shared by Chromium and Blink
   bindings. This can be de-duplicated in future CLs.


Cr-Commit-Position: refs/heads/master@{#421674}
48 files changed