Removed mtune for Android build.

build/config/arm.gni

 # Copyright 2014 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.
 
 declare_args() {
   # Version of the ARM processor when compiling on ARM. Ignored on non-ARM
   # platforms.
   arm_version = 7
 
   # The ARM floating point mode. This is either the string "hard", "soft", or
@@ skipping 22 matching lines @@
   if (arm_float_abi == "") {
     arm_float_abi = "softfp"
   }
   arm_fpu = "vfp"
   # Thumb is a reduced instruction set available on some ARM processors that
   # has increased code density.
   arm_use_thumb = false
 
 } else if (arm_version == 7) {
   arm_arch = "armv7-a"
-  arm_tune = "cortex-a8"
+  arm_tune = ""
   if (arm_float_abi == "") {
     arm_float_abi = "softfp"
   }
   arm_use_thumb = true
 
   if (arm_use_neon) {
     arm_fpu = "neon"
   } else {
     arm_fpu = "vfpv3-d16"
   }
 }