gn: add Blink GC plugin options
The Blink GC clang plugin supports a couple of extra options which the
Blink GN configuration does not currently expose. Do so here, but without
depending on the 'flags' script used by the gyp build system
(tools/clang/scripts/blink_gc_plugin_flags.py).
Specifically, this adds the following Blink GN variables:
- blink_gc_plugin_option_do_dump_graph [ = false ]
emit JSON-serialized representation of class graph.
- blink_gc_plugin_option_warn_unneeded_finalizer [ = false ]
warn of unnecessary destructor usage.
TBR=thakis
BUG=
Review-Url: https://codereview.chromium.org/2097433002
Cr-Commit-Position: refs/heads/master@{#401568}
3 files changed
