Clear reference to the IIntentReceiver in order to avoid memory leak

When using sendOrderedBroadcast(..) with a BroadcastReceiver the
BroadcastReceiver instance was not released. The reason for this was that
the resultTo field in the BroadcastRecord kept a reference until it was pushed
out of the mBroadcastHistory. This reference in turn kept a reference to the
process side IIntentReceiver (implemented in ReceiverDispatcher$InnerReceiver).
This in turn had a strong reference (through mStrongRef) to the Context.

In order to keep the debug output the resultTo is also kept as a String in the
new resultToString variable.

Change-Id: I4382a22a541c27b3694fb2b78a04ee820b235f8f

Author: Johannes Carlsson

services/java/com/android/server/am/ActivityManagerService.java

@@ -11035,6 +11035,9 @@ private final void processNextBroadcast(boolean fromMsg) {
                             performReceiveLocked(r.callerApp, r.resultTo,
                                 new Intent(r.intent), r.resultCode,
                                 r.resultData, r.resultExtras, false, false);
+                            // Set this to null so that the reference
+                            // (local and remote) isnt kept in the mBroadcastHistory.
+                            r.resultTo = null;
                         } catch (RemoteException e) {
                             Slog.w(TAG, "Failure sending broadcast result of " + r.intent, e);
                         }

services/java/com/android/server/am/BroadcastRecord.java

@@ -45,7 +45,7 @@ class BroadcastRecord extends Binder {
     final boolean initialSticky; // initial broadcast from register to sticky?
     final String requiredPermission; // a permission the caller has required
     final List receivers;   // contains BroadcastFilter and ResolveInfo
-    final IIntentReceiver resultTo; // who receives final result if non-null
+    IIntentReceiver resultTo; // who receives final result if non-null
     long dispatchTime;      // when dispatch started on this set of receivers
     long receiverTime;      // when current receiver started for timeouts.
     long finishTime;        // when we finished the broadcast.