Fix loss of texture filtering on <canvas> after getImageData call

Adding a texture state reset after a call toSkCanvas->readPixels,
which may alter the the GL texture parameters of the backing store
whithout the compositor being aware of it.

BUG=382588
TEST=layout test virtual/gpu/fast/canvas/bug382588.html

Review URL: https://codereview.chromium.org/339243003

git-svn-id: svn://svn.chromium.org/blink/trunk@176623 bbb929c8-8fbe-4397-9dbb-9b2b20218538