Switch to 35mm headphone and mic by priority when they are hot plugged.

Bug: 849594
Change-Id: Idcfd987a4e2d3357a81905b1f003ab1e81302298
Reviewed-on: https://chromium-review.googlesource.com/1087749Reviewed-by: Jenny Zhang <jennyz@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Jenny Zhang <jennyz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#564945}

chromeos/audio/cras_audio_handler.cc

@@ -1247,7 +1247,7 @@ void CrasAudioHandler::HandleHotPlugDevice(
   // device.
   if (hotplug_device.type == AUDIO_TYPE_HEADPHONE ||
       hotplug_device.type == AUDIO_TYPE_MIC) {
-    SwitchToDevice(hotplug_device, true, ACTIVATE_BY_USER);
+    SwitchToDevice(hotplug_device, true, ACTIVATE_BY_PRIORITY);
     return;
   }