Show correct call buttons depending on voice/video call.

Behaviors to be implemented in separate changelist.

Renamed some of the methods to reference buttons, and rearranged the
order in which buttons are listed and dealt with to be more
consistent with the order in the layout.

Bug: 16014280
Change-Id: I40a9137d222daf6959a869c11e6ac763baa61788
diff --git a/InCallUI/res/values/strings.xml b/InCallUI/res/values/strings.xml
index 3795aa5..dbbfc12 100644
--- a/InCallUI/res/values/strings.xml
+++ b/InCallUI/res/values/strings.xml
@@ -303,9 +303,9 @@
     <!-- Text for the onscreen "Video call" button used to change a voice call
          to a video call. [CHAR LIMIT=10] -->
     <string name="onscreenVideoCallText">Video call</string>
-    <!-- Text for the onscreen "Change to audio" button. When clicked, this downgrades a video call
-         to an audio call. -->
-    <string name="onscreenChangeToAudioText">Change to audio call</string>
+    <!-- Text for the onscreen "Change to voice" button. When clicked, this downgrades a video call
+         to a voice call. -->
+    <string name="onscreenChangeToVoiceText">Change to voice call</string>
     <!-- Text for the onscreen "Switch camera" button. When clicked, this switches the user's camera
          for video calling between the front-facing camera and the back-facing camera. -->
     <string name="onscreenSwitchCameraText">Switch camera</string>