[Android WebView] Tracing API: add trace argument filtering by default.

MERGE to M65

Add filtering of trace arguments data by default to the WebView Tracing
API. Only specifically whitelisted strings are allowed in trace args
to avoid exposing any potential PII and address privacy concerns.

Currently only a few metadata category events are whitelisted, e.g.
the "process_name", "thread_name" arguments which are useful for
viewing in "chrome://tracing".

BUG=804414

Change-Id: I1477cd363d36cd9a3b5cf3c6bd4de0e8a3a63e63
Reviewed-on: https://chromium-review.googlesource.com/879144
Commit-Queue: Tim Volodine <timvolodine@chromium.org>
Reviewed-by: Richard Coles <torne@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#531609}(cherry picked from commit 4595b036c1f527b31ec3279759b6e2bcdfca2084)
Reviewed-on: https://chromium-review.googlesource.com/929021
Reviewed-by: Tim Volodine <timvolodine@chromium.org>
Cr-Commit-Position: refs/branch-heads/3325@{#532}
Cr-Branched-From: bc084a8b5afa3744a74927344e304c02ae54189f-refs/heads/master@{#530369}
5 files changed