commit dcd255e349c35228be35f2f43232a2b1c5605e80
author Camillo Bruni <cbruni@chromium.org> Thu Oct 14 15:50:05 2021
committer Chromium LUCI CQ <chromium-scoped@luci-project-accounts.iam.gserviceaccount.com> Thu Oct 14 15:50:05 2021
tree db0856993fe5c9da914349ef818d97c68c2e2782
parent 86df2cc7769f56f91ff36538aa4db30c3e7a23c8

[flags] Make --js-flags settings have priority over V8 features

- Move --js-flags handling from the RenderProcessImpl constructor
  to a late stage in gin::V8Initializer::Initialize where they can
  override previously set flags
- Move content::switches::kJavaScriptFlags to blink::switches
- Allow blink_initializer.cc to access base::CommandLine to pass
  --js-flags to V8

V8 engineers are used to provide command-line flags manually.
For local testing it can be quite confusing if the flags conflict
with finch / field trial settings.
This CL changes the priority of --js-flags to be able to override
any flags previously set by features.

V8Flags are mostly initialized in two place:
1. content::RenderProcessImpl::RenderProcessImpl
2. gin::V8Initializer::Initialize

V8 flags are per-process globals, many of them should not be changed
after initialising V8. Thus the latest safe point to set V8 flags is
in gin::V8Initializer::Initialize.

Currently some flags are set in the RenderProcessImpl constructors,
especially --js-flags is processed there. With V8::SetFlagsFromString
the last flag takes precedence. As a result chrome feature flags that
are processed (late) in gin could not be overridden with --js-flags.

Bug: v8:12309
Change-Id: I832c274e760bf9bd61f9bf3fa8d7fc00251b4685
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3208413
Reviewed-by: Wez <wez@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Elad Alon <eladalon@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Finnur Thorarinsson <finnur@chromium.org>
Owners-Override: Wez <wez@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#931522}