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This adds chart GEM objects number and size to memory diagram.

TEST=Locally + limited unit tests
BUG=b:122555793

Change-Id: I902c65a016f89041e69ab202f6344eff9838a9dd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1592709Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Yury Khmel <khmel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#656250}