transcoding: Add a new API for client to add UID for a session.

This is needed for MediaProvider to append a UID to an existing
transcoding session when there are multiple client waiting
for the file to be transcoded.

Bug: 171398942
Test: atest  CtsMediaTranscodingTestCases:MediaTranscodeManagerTest
Change-Id: I58e561f7afed16314349764195a65386d1d0b909

apex/media/framework/api/system-current.txt

@@ -25,7 +25,9 @@ package android.media {
   }
 
   public static final class MediaTranscodeManager.TranscodingSession {
+    method public void addClientUid(int);
     method public void cancel();
+    method @NonNull public java.util.List<java.lang.Integer> getClientUids();
     method public int getErrorCode();
     method @IntRange(from=0, to=100) public int getProgress();
     method public int getResult();

apex/media/framework/java/android/media/MediaTranscodeManager.java

@@ -1352,6 +1352,8 @@ public final class MediaTranscodeManager {
         private @TranscodingSessionErrorCode int mErrorCode = ERROR_NONE;
         @GuardedBy("mLock")
         private boolean mHasRetried = false;
+        @GuardedBy("mLock")
+        private @NonNull List<Integer> mClientUidList = new ArrayList<>();
         // The original request that associated with this session.
         private final TranscodingRequest mRequest;
 
@@ -1370,6 +1372,7 @@ public final class MediaTranscodeManager {
             mListenerExecutor = executor;
             mListener = listener;
             mRequest = request;
+            mClientUidList.add(request.getClientUid());
         }
 
         /**
@@ -1514,6 +1517,36 @@ public final class MediaTranscodeManager {
             }
         }
 
+        /**
+         * Adds a client uid that is also waiting for this transcoding session.
+         * <p>
+         * Only privilege caller with android.permission.WRITE_MEDIA_STORAGE could add the
+         * uid. Note that the permission check happens on the service side upon starting the
+         * transcoding. If the client does not have the permission, the transcoding will fail.
+         */
+        public void addClientUid(int uid) {
+            if (uid < 0) {
+                throw new IllegalArgumentException("Invalid Uid");
+            }
+            synchronized (mLock) {
+                if (!mClientUidList.contains(uid)) {
+                    // see ag/14023202 for implementation
+                    mClientUidList.add(uid);
+                }
+            }
+        }
+
+        /**
+         * Query all the client that waiting for this transcoding session
+         * @return a list containing all the client uids.
+         */
+        @NonNull
+        public List<Integer> getClientUids() {
+            synchronized (mLock) {
+                return mClientUidList;
+            }
+        }
+
         /**
          * Gets sessionId of the transcoding session.
          * @return session id.