Move setIsInCanvasSubtree from attach/detach to insertedInto/removedFrom.

BUG=none

Review URL: https://chromiumcodereview.appspot.com/22532008

git-svn-id: svn://svn.chromium.org/blink/trunk@155765 bbb929c8-8fbe-4397-9dbb-9b2b20218538