[telemetry] Add support for requesting memory dumps via DevTools API

This (together with the proposed Tracing.dumpMemory DevTools API, see
https://docs.google.com/document/d/190-URzSjfsiXNeyke86z85-5ctuqsC_RoX1J1uJTwIQ/edit?usp=sharing)
will allow telemetry memory page interactions to request memory dumps
as follows:

  action_runner.tab.browser.DumpMemory()

BUG=505826

Review URL: https://codereview.chromium.org/1224083015

Cr-Commit-Position: refs/heads/master@{#340943}
6 files changed