This CL is a precursor to the callback-based enumeration of frame summaries.
It removes the reliance of FrameInspector on having a cached copy of the
FrameSummary, instead unpacking it to instance variables so that clients
of FrameInspector do not need to get information from two sources
(the FrameSummary and the FrameInspector itself).

R=yangguo@chromium.org

Bug: 
Change-Id: Ib388566c2e1a1147ee0a581323932982a29ae4ff
Reviewed-on: https://chromium-review.googlesource.com/618334
Commit-Queue: Ben Titzer <titzer@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47420}