Add an optimize_for_fuzzing GN flag to build with -O1

build/config/compiler/compiler.gni

 # Copyright 2015 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.
 
 import("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/toolchain/goma.gni")
 import("//build/toolchain/toolchain.gni")
@@ skipping 29 matching lines @@
   is_win_fastlink = false
 
   # Specify the current PGO phase, only used for the Windows MSVS build. Here's
   # the different values that can be used:
   #     0 : Means that PGO is turned off.
   #     1 : Used during the PGI (instrumentation) phase.
   #     2 : Used during the PGO (optimization) phase.
   #
   # TODO(sebmarchand): Add support for the PGU (update) phase.
   chrome_pgo_phase = 0
+
+  # Optimize for coverage guided fuzzing (balance between speed and number of
+  # branches)
+  optimize_for_fuzzing = false

[Dirk Pranke, 2016/10/03 20:37:13]

If this doesn't need to be referenced outside of
//build/config/compiler/BUILD.gn, you should put this in the declare_args()
block in that file.

[Oliver Chang, 2016/10/03 20:54:25]

Done.

 }
 
 declare_args() {
   # Whether or not the official builds should be built with full WPO. Enabled by
   # default for the PGO and the x64 builds.
   if (chrome_pgo_phase > 0) {
     full_wpo_on_official = true
   } else {
     full_wpo_on_official = false
   }
@@ skipping 41 matching lines @@
   } else {
     symbol_level = 0
   }
 }
 
 # Assert that the configuration isn't going to hit https://crbug.com/648948.
 assert(!is_android || android_64bit_target_cpu || is_component_build ||
            symbol_level < 2,
        "Android 32-bit non-component builds cannot have symbol_level=2 " +
            "due to 4GiB file size limit, see https://crbug.com/648948")