aura: Update UpdateRootWindowSizeInPixels() not take any input.

UpdateRootWindowSizeInPixels() should always use the pixel-bounds it
already knows about. So it does not need to take any input params. Fix
extension-shell to use SetBoundsInPixels() instead, because that's the
correct way to set the size of the host (which would automatically
update the size of the root-window etc.).

BUG=821987

Change-Id: I31d0e5fa21471192aab5c462f79a1b1906ec23ac
Reviewed-on: https://chromium-review.googlesource.com/1006491
Commit-Queue: Sadrul Chowdhury <[email protected]>
Reviewed-by: Scott Violet <[email protected]>
Cr-Commit-Position: refs/heads/master@{#550037}
4 files changed