GitLab

 - Introducing a new CSS attribute 'skip-search' to mark elements that should be
   ignored.
 - Modifying searching algorithm, to skip such elements, both when searching but
   also when triggering a forced rendering.
 - Modify <settings-animated-pages> to carry over the 'skip-search' attribute
   from the <template is="dom-if"> to the <settings-subpage> stamped instance.
 - Remove settings-subpage's noAssociatedControl member variable since it is not
   necessary anymore.

BUG=635017
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2217403002
Cr-Commit-Position: refs/heads/master@{#410432}