Fix audio focus evaluation order for display update

Change 1f9196a introduced
 an issue when trying to ignore audio focus entries in the
 stack that don't use the music stream, or are for transient
 audio focus gain, for remote control display updates.
The bug was that the audio focus stack traversal was not
 starting from the top, as it should. It was using
 the iterator order, which, in the case of a stack, starts
 with the bottom-most entry.
The fix consists in traversing the stack from the top, i.e.
 from the last element of the vector used to hold the stack
 entries.

Bug 7311023

Change-Id: I0c1900dbf98599a621a420ab55531a3eee838fe5

Author: jmtrivi

media/java/android/media/AudioService.java

@@ -5088,18 +5088,23 @@ private void checkUpdateRemoteControlDisplay_syncAfRcs(int infoChangedFlags) {
         // top of the stack for the media button event receivers : simply using the top of the
         // stack would make the entry disappear from the RemoteControlDisplay in conditions such as
         // notifications playing during music playback.
-        // crawl the AudioFocus stack until an entry is found with the following characteristics:
+        // Crawl the AudioFocus stack from the top until an entry is found with the following
+        // characteristics:
         // - focus gain on STREAM_MUSIC stream
         // - non-transient focus gain on a stream other than music
         FocusStackEntry af = null;
-        Iterator<FocusStackEntry> stackIterator = mFocusStack.iterator();
-        while(stackIterator.hasNext()) {
-            FocusStackEntry fse = (FocusStackEntry)stackIterator.next();
-            if ((fse.mStreamType == AudioManager.STREAM_MUSIC)
-                    || (fse.mFocusChangeType == AudioManager.AUDIOFOCUS_GAIN)) {
-                af = fse;
-                break;
+        try {
+            for (int index = mFocusStack.size()-1; index >= 0; index--) {
+                FocusStackEntry fse = mFocusStack.elementAt(index);
+                if ((fse.mStreamType == AudioManager.STREAM_MUSIC)
+                        || (fse.mFocusChangeType == AudioManager.AUDIOFOCUS_GAIN)) {
+                    af = fse;
+                    break;
+                }
             }
+        } catch (ArrayIndexOutOfBoundsException e) {
+            Log.e(TAG, "Wrong index accessing audio focus stack when updating RCD: " + e);
+            af = null;
         }
         if (af == null) {
             clearRemoteControlDisplay_syncAfRcs();
@@ -5120,6 +5125,7 @@ private void checkUpdateRemoteControlDisplay_syncAfRcs(int infoChangedFlags) {
             clearRemoteControlDisplay_syncAfRcs();
             return;
         }
+
         // refresh conditions were verified: update the remote controls
         // ok to call: synchronized mAudioFocusLock then on mRCStack, mRCStack is not empty
         updateRemoteControlDisplay_syncAfRcs(infoChangedFlags);