Use the new "optimize_speed" GN config.

gni/v8.gni

 # Copyright 2016 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/v8_target_cpu.gni")
+import("//build/config/sanitizers/sanitizers.gni")
 
 declare_args() {
   # Turns on compiler optimizations in V8 in Debug build.
   v8_optimized_debug = true
 
   # Enable the snapshot feature, for fast context creation.
   # http://v8project.blogspot.com/2015/09/custom-startup-snapshots.html
   v8_use_snapshot = true
 
   # Use external files for startup data blobs:
@@ skipping 16 matching lines @@
   "//build/config/compiler:no_chromium_code",
   path_prefix + ":features",
   path_prefix + ":toolchain",
 ]
 
 if (is_debug && !v8_optimized_debug) {
   remove_configs += [ "//build/config/compiler:default_optimization" ]
   add_configs += [ "//build/config/compiler:no_optimize" ]
 } else {
   remove_configs += [ "//build/config/compiler:default_optimization" ]
-  add_configs += [ "//build/config/compiler:optimize_max" ]
+
+  # TODO(crbug.com/621335) Rework this so that we don't have the confusion
+  # between "optimize_speed" and "optimize_max".
+  if (is_posix && !is_android && !is_nacl && !using_sanitizer) {
+    add_configs += [ "//build/config/compiler:optimize_speed" ]
+  } else {
+    add_configs += [ "//build/config/compiler:optimize_max" ]
+  }
 }
 
 # All templates should be kept in sync.
 template("v8_source_set") {
   source_set(target_name) {
     forward_variables_from(invoker, "*", [ "configs" ])
     configs += invoker.configs
     configs -= remove_configs
     configs += add_configs
   }
 }
 
 template("v8_executable") {
   executable(target_name) {
     forward_variables_from(invoker, "*", [ "configs" ])
     configs += invoker.configs
     configs -= remove_configs
     configs += add_configs
   }
 }
 
 template("v8_component") {
   component(target_name) {
     forward_variables_from(invoker, "*", [ "configs" ])
     configs += invoker.configs
     configs -= remove_configs
     configs += add_configs
   }
 }