ozone: ClientPixmapManager passes VGEM fd from browser to renderer.

Browser and Renderer have the singleton ClientPixmapManager instance.
BrowserClientPixmapManager and ChildClientPixmapManager communicates
via existing Browser-Renderer IPC to transfer virtual device FD.
e.g. VGEM FD in Ozone GBM

Browser sends virtual device fd to all renderers when the channel
is established. Renderer creates the singleton ChildClientPixmapManager
at the time. It's similar to how MACOSX shares |io_surface_manager_token_|.

BUG=475633

Review URL: https://codereview.chromium.org/1248713002

Cr-Commit-Position: refs/heads/master@{#346433}
15 files changed