Use monotonic raw timestamp by default except for x86/64

chromecast/media/cma/backend/alsa/BUILD.gn

 # 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/buildflag_header.gni")
 import("//media/media_options.gni")
 import("//testing/test.gni")
 
 declare_args() {
-  # Set true to use raw timestamps. This should only be enabled when the ALSA
-  # library supports it.
   use_alsa_monotonic_raw_tstamps = false
+
+  # Set true to use raw timestamps except on x86 and x64 platforms.
+  # Alsa version equal or later than 1.0.29 support this function.
+  if (!is_cast_desktop_build) {

[slan, 2016/03/16 16:55:26]

This condition is not needed, please just declare it like this:

use_alsa_monotonic_raw_tstamps = !is_cast_desktop_build

[slan, 2016/03/16 16:58:47]

P.S. For good style, let's add this to the top:

import("//build/config/chromecast_build.gni")

This is recursively imported via media_options.gni, but I think Include What You
Use is a good policy here.

[mengyu1, 2016/03/16 16:59:55]

Done.

[mengyu1, 2016/03/16 17:04:59]

Done. Sorry, didn't see this import comment previously.

+    use_alsa_monotonic_raw_tstamps = true
+  }
 }
 
 # Alsa must be used for these targets to build.
 assert(use_alsa)
 
 # GYP target: chromecast/media/media.gyp:libcast_media_1.0_audio
 shared_library("libcast_media_1.0_audio") {
   sources = [
     "//chromecast/media/base/media_caps.cc",
     "//chromecast/media/base/media_caps.h",
@@ skipping 77 matching lines @@
   public_deps = [
     ":alsa_cma_backend",
   ]
 
   deps = [
     "//base",
     "//media",
     "//testing/gmock",
   ]
 }