Also check for home activity in BAL

Since checking for home process can fail if lancher has been killed but
we still want to allow launcher to start activities.

Bug: 189896361
Test: 1. Set app 1 as launcher, give PI for random activity to app 2
      2. With app 2 in fg, kill app 1
      3. Launch PI, verify it launches
Change-Id: Ia5eb5bfcf239b6dd2f732516edeac29a77c8a478

services/core/java/com/android/server/wm/ActivityStarter.java

@@ -87,6 +87,7 @@ import android.app.IApplicationThread;
 import android.app.PendingIntent;
 import android.app.ProfilerInfo;
 import android.app.WaitResult;
+import android.content.ComponentName;
 import android.content.IIntentSender;
 import android.content.Intent;
 import android.content.IntentSender;
@@ -1222,6 +1223,20 @@ class ActivityStarter {
         mController.onExecutionComplete(this);
     }
 
+    private boolean isHomeApp(int uid, @Nullable String packageName) {
+        if (mService.mHomeProcess != null) {
+            // Fast check
+            return uid == mService.mHomeProcess.mUid;
+        }
+        if (packageName == null) {
+            return false;
+        }
+        ComponentName activity =
+                mService.getPackageManagerInternalLocked().getDefaultHomeActivity(
+                        UserHandle.getUserId(uid));
+        return activity != null && packageName.equals(activity.getPackageName());
+    }
+
     boolean shouldAbortBackgroundActivityStart(int callingUid, int callingPid,
             final String callingPackage, int realCallingUid, int realCallingPid,
             WindowProcessController callerApp, PendingIntentRecord originatingPendingIntent,
@@ -1237,7 +1252,7 @@ class ActivityStarter {
         }
 
         // Always allow home application to start activities.
-        if (mService.mHomeProcess != null && callingUid == mService.mHomeProcess.mUid) {
+        if (isHomeApp(callingUid, callingPackage)) {
             if (DEBUG_ACTIVITY_STARTS) {
                 Slog.d(TAG, "Activity start allowed for home app callingUid (" + callingUid + ")");
             }

services/tests/wmtests/src/com/android/server/wm/ActivityStarterTests.java

@@ -348,6 +348,7 @@ public class ActivityStarterTests extends WindowTestsBase {
                 invocation -> {
                     throw new RuntimeException("Not stubbed");
                 });
+        doReturn(null).when(mMockPackageManager).getDefaultHomeActivity(anyInt());
         doReturn(mMockPackageManager).when(mAtm).getPackageManagerInternalLocked();
         doReturn(false).when(mMockPackageManager).isInstantAppInstallerComponent(any());
         doReturn(null).when(mMockPackageManager).resolveIntent(any(), any(), anyInt(), anyInt(),