Set V8 extras mode in gin::V8Initializer.

third_party/WebKit/Source/bindings/core/v8/V8Initializer.cpp

Index: third_party/WebKit/Source/bindings/core/v8/V8Initializer.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/V8Initializer.cpp b/third_party/WebKit/Source/bindings/core/v8/V8Initializer.cpp
index 0372286eb9b38e55eff4179f5416e71438d7ffad..823f5f2d6dd9c24fe69ee69f5f2539a61ba02eb7 100644
--- a/third_party/WebKit/Source/bindings/core/v8/V8Initializer.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/V8Initializer.cpp
@@ -385,7 +385,8 @@ void V8Initializer::initializeMainThreadIfNeeded()
     initialized = true;
 
     DEFINE_STATIC_LOCAL(ArrayBufferAllocator, arrayBufferAllocator, ());
-    gin::IsolateHolder::Initialize(gin::IsolateHolder::kNonStrictMode, &arrayBufferAllocator);
+    auto v8ExtrasMode = RuntimeEnabledFeatures::experimentalV8ExtrasEnabled() ? gin::IsolateHolder::kStableAndExperimentalV8Extras : gin::IsolateHolder::kStableV8Extras;
+    gin::IsolateHolder::Initialize(gin::IsolateHolder::kNonStrictMode, v8ExtrasMode, &arrayBufferAllocator);
 
     v8::Isolate* isolate = V8PerIsolateData::initialize();