MediaRouter: don't scanPackages if unnecessary

scanPackages was called whenever it receives a broadcast,
which could be duplicated.
This CL adds a boolean variable (mScanPackagesScheduled) not
to scan packages if it is scheduled.

Bug: 153527463
Test: cts test, atest mediarouertest and check
MediaRouteProvider#onBind, #onUnbind are called
when a new provider is installed.
Confirm # of calls is reduced (3 -> 1).

Change-Id: Iaa423b7d1b2b2a97aebed0001b4077bdf95b1d54

services/core/java/com/android/server/media/MediaRoute2ProviderServiceProxy.java

@@ -169,6 +169,8 @@ final class MediaRoute2ProviderServiceProxy extends MediaRoute2Provider
     }
 
     public void rebindIfDisconnected() {
+        //TODO: When we are connecting to the service, calling this will unbind and bind again.
+        // We'd better not unbind if we are connecting.
         if (mActiveConnection == null && shouldBind()) {
             unbind();
             bind();

services/core/java/com/android/server/media/MediaRoute2ProviderWatcher.java

@@ -83,7 +83,7 @@ final class MediaRoute2ProviderWatcher {
 
             // Scan packages.
             // Also has the side-effect of restarting providers if needed.
-            mHandler.post(mScanPackagesRunnable);
+            postScanPackagesIfNeeded();
         }
     }
 
@@ -92,7 +92,7 @@ final class MediaRoute2ProviderWatcher {
             mRunning = false;
 
             mContext.unregisterReceiver(mScanPackagesReceiver);
-            mHandler.removeCallbacks(mScanPackagesRunnable);
+            mHandler.removeCallbacks(this::scanPackages);
 
             // Stop all providers.
             for (int i = mProxies.size() - 1; i >= 0; i--) {
@@ -154,20 +154,19 @@ final class MediaRoute2ProviderWatcher {
         return -1;
     }
 
+    private void postScanPackagesIfNeeded() {
+        if (!mHandler.hasCallbacks(this::scanPackages)) {
+            mHandler.post(this::scanPackages);
+        }
+    }
+
     private final BroadcastReceiver mScanPackagesReceiver = new BroadcastReceiver() {
         @Override
         public void onReceive(Context context, Intent intent) {
             if (DEBUG) {
                 Slog.d(TAG, "Received package manager broadcast: " + intent);
             }
-            scanPackages();
-        }
-    };
-
-    private final Runnable mScanPackagesRunnable = new Runnable() {
-        @Override
-        public void run() {
-            scanPackages();
+            postScanPackagesIfNeeded();
         }
     };