Web MIDI: link with alsa even if cras is enabled

This CL fixes a feature breakage on Chrome OS which happens by
crrev.com/244251 accidentally.

Chrome for Chrome OS should be linked with alsa even if cras is enabled.
This is because Web MIDI implementation for Chrome OS depends on alsa.

Also this changes add trace events for each platform implementation.
This is also useful to know which implementation is enabled in the build.

BUG=335865

Review URL: https://codereview.chromium.org/171603014

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253373 0039d316-1c4b-4281-b951-d872f2087c98
Modify chrome.streamsPrivate to provide a single object as the parameter

BUG=345882

Review URL: https://codereview.chromium.org/175593006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253374 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253373
Add better error message for requestAutocomplete when API key is bad.

This is not something a typical user should ever see, but assists developers in debugging.

BUG=none

Review URL: https://codereview.chromium.org/178743004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253375 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253375