Correct negative sub-pixel offset handling in composited layers

Code in CompositedLayerMapping used flooredIntPoint in an attempt
to represent an offset with the sub-pixel fraction removed.
Unfortunately, flooring a negative number with a sub-pixel fraction
will floor down to the next negative value, which isn't what the
code wanted. Changing it to use toInt() instead, which has the
effect of truncating the values.

BUG=362889

Review URL: https://codereview.chromium.org/240453003

git-svn-id: svn://svn.chromium.org/blink/trunk@171805 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Mark virtual/gpu/fast/canvas/canvas-composite-text-alpha.html as slow

TBR=junov@chromium.org
BUG=

Review URL: https://codereview.chromium.org/238983008

git-svn-id: svn://svn.chromium.org/blink/trunk@171806 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove WebScreenOrientation.h

BUG=162827

Review URL: https://codereview.chromium.org/238313002

git-svn-id: svn://svn.chromium.org/blink/trunk@171807 bbb929c8-8fbe-4397-9dbb-9b2b20218538