Use "-Os" for Android or IOS in "optimize_max" config

build/config/compiler/BUILD.gn

 # Copyright (c) 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.
 
 import("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/toolchain.gni")
@@ skipping 1391 matching lines @@
           "/GL",  # Whole program optimization.
 
           # Disable Warning 4702 ("Unreachable code") for the WPO/PGO builds.
           # Probably anything that this would catch that wouldn't be caught in a
           # normal build isn't going to actually be a bug, so the incremental
           # value of C4702 for PGO builds is likely very small.
           "/wd4702",
         ]
       }
     } else {
-      cflags = [ "-O2" ] + common_optimize_on_cflags
+      if (optimize_for_size) {
+        cflags = [ "-Os" ] + common_optimize_on_cflags
+      } else {
+        cflags = [ "-O2" ] + common_optimize_on_cflags
+      }
     }
   }
 }
 
 # This config can be used to override the default settings for per-component
 # and whole-program optimization, optimizing the particular target for speed
 # instead of code size. This config is exactly the same as "optimize_max"
 # except that we use -O3 instead of -O2 on non-win, non-IRT platforms.
 #
 # TODO(crbug.com/621335) - rework how all of these configs are related
@@ skipping 144 matching lines @@
 
 if (is_ios || is_mac) {
   # On Mac and iOS, this enables support for ARC (automatic ref-counting).
   # See http://clang.llvm.org/docs/AutomaticReferenceCounting.html.
   config("enable_arc") {
     common_flags = [ "-fobjc-arc" ]
     cflags_objc = common_flags
     cflags_objcc = common_flags
   }
 }