[Chromecast] Set use_alsa=true by default on Chromecast platforms.

media/media.gyp

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     'chromium_code': 1,
     # Override to dynamically link the cras (ChromeOS audio) library.
     'use_cras%': 0,
     # Option e.g. for Linux distributions to link pulseaudio directly
     # (DT_NEEDED) instead of using dlopen. This helps with automated
     # detection of ABI mismatches and prevents silent errors.
     'linux_link_pulseaudio%': 0,
     'conditions': [
       # Enable ALSA and Pulse for runtime selection.
-      ['(OS=="linux" or OS=="freebsd" or OS=="solaris") and ((embedded!=1 and chromecast==0) or is_cast_desktop_build==1)', {
+      ['(OS=="linux" or OS=="freebsd" or OS=="solaris") and (embedded==0 or chromecast==1)', {

[alokp, 2016/02/10 06:03:13]

I am curious about the difference between gyp and gn. GN does not use embedded
flag?

[slan, 2016/02/10 16:05:23]

I *thought* that |embedded| was not used by builds other than Chromecast, but I
found out that that was an incorrect assumption the last time I touched this
file (https://codereview.chromium.org/1530713006), so I'm being proactive.
|embedded| will not be ported to GN. 

         # ALSA is always needed for Web MIDI even if the cras is enabled.
         'use_alsa%': 1,
         'conditions': [
-          ['use_cras==1', {
+          ['use_cras==1 or chromecast==1', {
             'use_pulseaudio%': 0,
           }, {
             'use_pulseaudio%': 1,
           }],
         ],
       }, {
         'use_alsa%': 0,
         'use_pulseaudio%': 0,
       }],
       # low memory buffer is used in non-Android based chromecast build due to hardware limitation.
@@ skipping 2112 matching lines @@
               'dependencies': [
                 '../tools/xdisplaycheck/xdisplaycheck.gyp:xdisplaycheck',
               ],
             }],
           ],
         },
       ],
     }],
   ],
 }