[css-typed-om] Add use counters to the StylePropertyMaps.

Adds use counters for declared/inline/computed StylePropertyMaps.
Any meaningful use of Typed OM requires using accessing these
StylePropertyMaps.

Bug: 545318
Change-Id: I627f4d2582a7a27361ee60ecd69ebf31498e693a
Reviewed-on: https://chromium-review.googlesource.com/866511
Commit-Queue: Darren Shen <shend@chromium.org>
Commit-Queue: nainar <nainar@chromium.org>
Reviewed-by: nainar <nainar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#529224}
6 files changed