Reland of FrameGenerator should not be created until an AcceleratedWidget is available (patchset #1 id:1 of https://codereview.chromium.org/2717453002/ )

Reason for revert:
This was not the culprit of crbug.com/695375 as the build bot results said. Sorry for confusion.

https://build.chromium.org/p/chromium.win/buildstatus?builder=Win7%20Tests%20%281%29&number=64018

Original issue's description:
> Revert of FrameGenerator should not be created until an AcceleratedWidget is available (patchset #6 id:100001 of https://codereview.chromium.org/2694043003/ )
>
> Reason for revert:
> This might cause the crash (crbug/695371)
>
> Original issue's description:
> > FrameGenerator should not be created until an AcceleratedWidget is available
> >
> > FrameGenerator does not have anything useful to do until an
> > AcceleratedWidget is provided. This CL delays the creation of
> > FrameGenerator until a widget is available.
> >
> > We also remove the unit test because it's not doing anything useful
> > right now.
> >
> > BUG=683732
> >
> > Review-Url: https://codereview.chromium.org/2694043003
> > Cr-Commit-Position: refs/heads/master@{#452329}
> > Committed: https://chromium.googlesource.com/chromium/src/+/c46bbe24124bdef62daa0e396bb4baa2681fd817
>
> TBR=fsamuel@chromium.org,sky@chromium.org,samans@chromium.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=683732
>
> Review-Url: https://codereview.chromium.org/2717453002
> Cr-Commit-Position: refs/heads/master@{#452446}
> Committed: https://chromium.googlesource.com/chromium/src/+/cfa63cc0384a8ab0d8dbea6e67543d21716485dd

TBR=fsamuel@chromium.org,sky@chromium.org,samans@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=683732

Review-Url: https://codereview.chromium.org/2715533006
Cr-Commit-Position: refs/heads/master@{#452457}
6 files changed