impl: Fix the spec_ and its size allocation

"2 * sizeof bounds.width()" for the size of spec_ is very wrong and, besides,
the format also needed to be changed for the correct one (something like
"%dx%d*2").

This changes here explicitly exposes the problem of OutputHandleMode not coming
in time during Chromium's initialization. But I'll be fixing it completely in
the upcoming commit.
impl: Make sure OzoneDisplay::spec_ is meant for browser UI only

Note that this patch and the previous fix the geometries of non-root windows.
So for instance, right-click in the address bar now open the cute menu as
expected.
ipc: Remove unused code from ChannelHost

OzoneDisplayChannelHost::UpdateConnection always need to be ran by the IO
thread channel.

And the second snip of code concerns some clean up just.
ipc: Remove channel identifier

The identifier was being superfluous in most of the cases and there's always
going to be one solely channel between the GPU IO thread and the one from the
browser. So I'm removing it.
Merge pull request #94 from 01org/ipc-cleanup-v2

Ipc cleanup