Revert "Make compositingState explicit (re-land with bogus ASSERT removed)"

This reverts commit 2a33ee04f3cb493d3081ef700fb12d6344c39cd4.

This change is hitting
"ASSERTION FAILED: layerChanged == compositingStateChanged"
in 100+ debug tests.

TBR=shawnsingh@chromium.org
NOTRY=TRUE

Review URL: https://codereview.chromium.org/26470002

git-svn-id: svn://svn.chromium.org/blink/trunk@159108 bbb929c8-8fbe-4397-9dbb-9b2b20218538