Avoid extra bitmap copies in SkColorSpaceXformCanvas

Before:
ColorCanvasDrawBitmap_sRGB_to_sRGB     5.09us
ColorCanvasDrawBitmap_AdobeRGB_to_sRGB 50.7us

After:
ColorCanvasDrawBitmap_sRGB_to_sRGB     2.43us
ColorCanvasDrawBitmap_AdobeRGB_to_sRGB 37.1us

BUG=skia:6456
Change-Id: Ie382936c36fd347b59485882cf8f27f315a5d35f

Change-Id: Ie382936c36fd347b59485882cf8f27f315a5d35f
Reviewed-on: https://skia-review.googlesource.com/11040
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Matt Sarett <msarett@google.com>
5 files changed