blink: Add MovableString for parkable strings, and use it for JS source.

This CL introduces MovableString to hold javascript string
resources. This class may move its data, although this CL only
introduces the simulation of it in order to gather data about such an
approach.

This CL is essentially a port of
https://codereview.chromium.org/1583263002 from hajimehoshi@. It has
been updated to the new conventions and coding style, but is otherwise
equivalent, with changes to histogram collection and triggering.

Bug: 837659,574317
Change-Id: I9028fd941f3d235761f10a2147ab21e31edac6d6
Reviewed-on: https://chromium-review.googlesource.com/1082445
Commit-Queue: Benoit L <lizeb@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572229}
28 files changed