Bump Chrome's deployment target to macOS 10.9.

build_overrides/build.gni

 # Copyright 2016 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.
 
 # Several dependencies of Chrome require a different min sdk and/or deployment
 # target when built as stand-alone projects. If this is ever not the case, these
 # variables can be removed.
 # See https://bugs.chromium.org/p/webrtc/issues/detail?id=5453.
 mac_sdk_min_build_override = "10.10"
-mac_deployment_target_build_override = "10.8"
+mac_deployment_target_build_override = "10.9"
 
 # Variable that can be used to support multiple build scenarios, like having
 # Chromium specific targets in a client project's GN file etc.
 build_with_chromium = true
 
 # Uncomment these to specify a different NDK location and version in
 # non-Chromium builds.
 # default_android_ndk_root = "//third_party/android_tools/ndk"
 # default_android_ndk_version = "r10e"
 
@@ skipping 10 matching lines @@
 
 # Uncomment these to specify a different lint suppressions file for android
 # lint_suppressions_file = path/to/your/suppressions/file/suppressions.xml
 
 declare_args() {
   # Android 32-bit non-component, non-clang builds cannot have symbol_level=2
   # due to 4GiB file size limit, see https://crbug.com/648948.
   # Set this flag to true to skip the assertion.
   ignore_elf32_limitations = false
 }