[Temp] Backport Chromium r249361.

Original author: joone.hur@intel.com

From the original commit message:

  Build fix when use_alsa=0.

  When use_alsa=0, there is a link error as follows:

  ../../media/audio/pulse/audio_manager_pulse.cc:81: error: undefined reference to 'media::AudioManagerAlsa::ShowLinuxAudioInputSettings()'
  collect2: error: ld returned 1 exit status
  ninja: build stopped: subcommand failed.

  This patch allows to add a guard to alsa related code to fix this link error.

  BUG=none

  Review URL: https://codereview.chromium.org/150573017

This commit is necessary while we disable Alsa support in Tizen; which is
necessary until TIVI-2685 doesn't make it into all Tizen profiles.
Merge pull request #122 from rakuco/no-alsa-backport

[Temp] Backport Chromium r249361.