Do DXVA init inside (lowered) gpu sandbox

On some drivers, the second D3D9 device creation stalls for long periods
of time. By deferring DXVA's until it's required, we can avoid the delay
at startup caused by DXVA + ANGLE both creating d3d devices at startup.
This is possible now, but wasn't before because of the lowering of the
gpu sandbox in http://crrev.com/233785 .

Also, some refactoring and cleanups since not needing pre-sandbox
initialization allows us to simplify a bit.

R=fischman@chromium.org, ananta@chromium.org
TBR=kbr@chromium.org
BUG=311259,270179

Review URL: https://codereview.chromium.org/79303003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236612 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236612
Converting unit test from using DCHECK to EXPECT macros (DCHECKs are compiled out in release mode on some bots, apparently, causing the test to fail in weird and wonderful ways).

BUG=318120, 321622
R=kalman@chromium.org

Review URL: https://codereview.chromium.org/81283002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236614 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236614