Enforce --disallow-v8-feature-flag-overrides in the renderer

This renderer command line switch is intended to prevent feature
flag overrides from configuring V8 flags.

To enforce this, v8 feature flag overrides have been conditioned on
this command line switch in the following locations:
  - content::RenderProcessImpl::RenderProcessImpl()
  - gin::SetFeatureFlags()

This change is intended to enable consistent V8 flags at build-time
and run-time, and hence compatibility for bundled code caches.

Bug: 388577282
Change-Id: Ifd2465cf54bc8353a2f33701157bc9be538eb777
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6144831
Commit-Queue: Thomas Lukaszewicz <tluk@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1407497}
diff --git a/gin/v8_initializer.h b/gin/v8_initializer.h
index 74e25c98..1341b77 100644
--- a/gin/v8_initializer.h
+++ b/gin/v8_initializer.h
@@ -30,8 +30,9 @@
  public:
   // This should be called by IsolateHolder::Initialize().
   static void Initialize(IsolateHolder::ScriptMode mode,
-                         const std::string& js_command_line_flags = {},
-                         v8::OOMErrorCallback oom_error_callback = nullptr);
+                         const std::string& js_command_line_flags,
+                         bool disallow_v8_feature_flag_overrides,
+                         v8::OOMErrorCallback oom_error_callback);
 
   // Get address and size information for currently loaded snapshot.
   // If no snapshot is loaded, the return values are null for addresses