Improve gpu texture recycling in Canvas2DLayerBridge.

Changing the allocation of the initaial SkSurface in
Canvas2DLayerBridge so that it may be taken from the GrContext
texture pool. This should improve performance for apps that
rely heavily on transient canvas objects.

BUG=351798

Review URL: https://codereview.chromium.org/196833006

git-svn-id: svn://svn.chromium.org/blink/trunk@169856 bbb929c8-8fbe-4397-9dbb-9b2b20218538