Fix value of pageScaleLayer registered with CC.
Fix value of pageScaleLayer registered with CC.

The current value of the page scale layer being registered with CC is incorrect; instead of passing the root layer, we should be passing the parent of the root scroll layer.

BUG=

Review URL: https://chromiumcodereview.appspot.com/23530061

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@157850 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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