[Gin] Add feature to control optimization in V8.

Change-Id: I7ff3a987d132d4ca8e0f350e851020b53d4fb009
Reviewed-on: https://chromium-review.googlesource.com/980947
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#546143}

gin/BUILD.gn

@@ -25,6 +25,8 @@ component("gin") {
     "function_template.cc",
     "function_template.h",
     "gin_export.h",
+    "gin_features.cc",
+    "gin_features.h",
     "handle.h",
     "interceptor.cc",
     "interceptor.h",

gin/gin_features.cc

@@ -0,0 +1,13 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "gin/gin_features.h"
+
+namespace features {
+
+// Enables optimization of JavaScript in V8.
+const base::Feature kV8OptimizeJavascript{"V8OptimizeJavascript",
+                                          base::FEATURE_ENABLED_BY_DEFAULT};
+
+}  // namespace features

gin/gin_features.h

@@ -0,0 +1,17 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef GIN_GIN_FEATURES_H_
+#define GIN_GIN_FEATURES_H_
+
+#include "base/feature_list.h"
+#include "gin/gin_export.h"
+
+namespace features {
+
+GIN_EXPORT extern const base::Feature kV8OptimizeJavascript;
+
+}  // namespace features
+
+#endif  // GIN_GIN_FEATURES_H_

gin/v8_initializer.cc

@@ -25,6 +25,7 @@
 #include "base/threading/platform_thread.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
+#include "gin/gin_features.h"
 
 #if defined(V8_USE_EXTERNAL_STARTUP_DATA)
 #if defined(OS_ANDROID)
@@ -242,6 +243,14 @@ void V8Initializer::Initialize(IsolateHolder::ScriptMode mode,
 
   v8::V8::InitializePlatform(V8Platform::Get());
 
+  if (base::FeatureList::IsEnabled(features::kV8OptimizeJavascript)) {
+    static const char optimize[] = "--opt";
+    v8::V8::SetFlagsFromString(optimize, sizeof(optimize) - 1);
+  } else {
+    static const char no_optimize[] = "--no-opt";
+    v8::V8::SetFlagsFromString(no_optimize, sizeof(no_optimize) - 1);
+  }
+
   if (IsolateHolder::kStrictMode == mode) {
     static const char use_strict[] = "--use_strict";
     v8::V8::SetFlagsFromString(use_strict, sizeof(use_strict) - 1);