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This CL reworks the trace generation format for the memory maps
dumper according to latest discussion in the design doc
"Memory Dumping: Mmap and Smap data dumping details"
(http://goo.gl/e6WRnQ).
Furthermore this CL changes the output format of the total dumper to
dump a hex string rather than a float, in order to be consistent with
the mmaps dumper.

See http://pastebin.com/EHdNDMXN for an example of the generated JSON.

BUG=460884

Review URL: https://codereview.chromium.org/947103003

Cr-Commit-Position: refs/heads/master@{#321570}