Revert r159961 (blink) "Defer the real work in updateCompositingLayers until it's really needed."

Assertions are being triggered on android GPU debug bots. Temporarily
reverting so that the bot can still cover all other CLs. I'm optimistic
the solution will be straightforward and this patch can re-land ASAP
after that.

BUG=309733
R=adamk@chromium.org
TBR=kbr@chromium.org, vollick@chromium.org

Review URL: https://codereview.chromium.org/32553004

git-svn-id: svn://svn.chromium.org/blink/trunk@160106 bbb929c8-8fbe-4397-9dbb-9b2b20218538