gin: Add a flag for a Finch experiment V8PerContextMarkingWorklist

The new feature flag passes --stress-per-context-marking-worklist flag
to V8, which instructs the GC to use per-context marking worklist.

Bug: 1038180
Change-Id: Ia7255e0ca70129cbaec7b568667a319cec8a743f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2089865Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#747656}

gin/gin_features.cc

@@ -22,4 +22,7 @@ const base::Feature kV8LazyFeedbackAllocation{"V8LazyFeedbackAllocation",
 const base::Feature kV8ConcurrentInlining{"V8ConcurrentInlining",
                                           base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Enable per-context marking worklists in V8 GC.
+const base::Feature kV8PerContextMarkingWorklist{
+    "V8PerContextMarkingWorklist", base::FEATURE_DISABLED_BY_DEFAULT};
 }  // namespace features

gin/gin_features.h

@@ -14,6 +14,7 @@ GIN_EXPORT extern const base::Feature kV8OptimizeJavascript;
 GIN_EXPORT extern const base::Feature kV8FlushBytecode;
 GIN_EXPORT extern const base::Feature kV8LazyFeedbackAllocation;
 GIN_EXPORT extern const base::Feature kV8ConcurrentInlining;
+GIN_EXPORT extern const base::Feature kV8PerContextMarkingWorklist;
 
 }  // namespace features
 

gin/v8_initializer.cc

@@ -225,6 +225,13 @@ void V8Initializer::Initialize(IsolateHolder::ScriptMode mode) {
                                sizeof(tf_experiment_concurrent_inlining) - 1);
   }
 
+  if (base::FeatureList::IsEnabled(features::kV8PerContextMarkingWorklist)) {
+    static const char stress_per_context_marking_worklist[] =
+        "--stress-per-context-marking-worklist";
+    v8::V8::SetFlagsFromString(stress_per_context_marking_worklist,
+                               sizeof(stress_per_context_marking_worklist) - 1);
+  }
+
   if (IsolateHolder::kStrictMode == mode) {
     static const char use_strict[] = "--use_strict";
     v8::V8::SetFlagsFromString(use_strict, sizeof(use_strict) - 1);