Use monotonic raw timestamp by default except for x86/64

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

Index: chromecast/media/cma/backend/alsa/BUILD.gn
diff --git a/chromecast/media/cma/backend/alsa/BUILD.gn b/chromecast/media/cma/backend/alsa/BUILD.gn
index c12367d8a9be472b2ef6d5c77ce0d89a342d24d5..7ea0ff21aeb9830d214c32a6120ed38a3b6a2601 100644
--- a/chromecast/media/cma/backend/alsa/BUILD.gn
+++ b/chromecast/media/cma/backend/alsa/BUILD.gn
@@ -7,9 +7,13 @@ 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.