[gin] Add V8IgnitionLowEnd experiment

gin/v8_initializer.cc

 // Copyright 2013 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/v8_initializer.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
 
 #include "base/debug/alias.h"
 #include "base/feature_list.h"
 #include "base/files/file.h"
 #include "base/files/file_path.h"
 #include "base/files/memory_mapped_file.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "base/rand_util.h"
 #include "base/strings/sys_string_conversions.h"
+#include "base/sys_info.h"
 #include "base/threading/platform_thread.h"
 #include "base/time/time.h"
 #include "crypto/sha2.h"
 #include "gin/public/gin_features.h"
 
 #if defined(V8_USE_EXTERNAL_STARTUP_DATA)
 #if defined(OS_ANDROID)
 #include "base/android/apk_assets.h"
 #endif
 #if defined(OS_MACOSX)
@@ skipping 190 matching lines @@
   return false;
 }
 #endif  // V8_VERIFY_EXTERNAL_STARTUP_DATA
 #endif  // V8_USE_EXTERNAL_STARTUP_DATA
 
 bool GenerateEntropy(unsigned char* buffer, size_t amount) {
   base::RandBytes(buffer, amount);
   return true;
 }
 
+bool ShouldUseIgnition() {
+  if (base::FeatureList::IsEnabled(features::kV8Ignition)) return true;
+#if defined(OS_ANDROID)
+  if (base::FeatureList::IsEnabled(features::kV8IgnitionLowEnd) &&
+      base::SysInfo::IsLowEndDevice()) {
+    return true;
+  }
+#endif
+  return false;
+}
+
+
 }  // namespace
 
 #if defined(V8_USE_EXTERNAL_STARTUP_DATA)
 #if defined(V8_VERIFY_EXTERNAL_STARTUP_DATA)
 // Defined in gen/gin/v8_snapshot_fingerprint.cc
 extern const unsigned char g_natives_fingerprint[];
 extern const unsigned char g_snapshot_fingerprint[];
 #endif  // V8_VERIFY_EXTERNAL_STARTUP_DATA
 
 enum LoadV8FileResult {
@@ skipping 181 matching lines @@
 
   if (IsolateHolder::kStrictMode == mode) {
     static const char use_strict[] = "--use_strict";
     v8::V8::SetFlagsFromString(use_strict, sizeof(use_strict) - 1);
   }
   if (IsolateHolder::kStableAndExperimentalV8Extras == v8_extras_mode) {
     static const char flag[] = "--experimental_extras";
     v8::V8::SetFlagsFromString(flag, sizeof(flag) - 1);
   }
 
-  if (base::FeatureList::IsEnabled(features::kV8Ignition)) {
+  if (ShouldUseIgnition()) {
     std::string flag("--ignition");
     v8::V8::SetFlagsFromString(flag.c_str(), static_cast<int>(flag.size()));
 
     if (base::FeatureList::IsEnabled(features::kV8IgnitionEager)) {
       std::string eager_flag("--ignition-eager");
       v8::V8::SetFlagsFromString(
           eager_flag.c_str(), static_cast<int>(eager_flag.size()));
     }
 
     if (base::FeatureList::IsEnabled(features::kV8IgnitionLazy)) {
@@ skipping 40 matching lines @@
     *snapshot_data_out =
         reinterpret_cast<const char*>(g_mapped_snapshot->data());
     *snapshot_size_out = static_cast<int>(g_mapped_snapshot->length());
   } else {
     *snapshot_data_out = NULL;
     *snapshot_size_out = 0;
   }
 }
 
 }  // namespace gin