Don't return null in the default ActivityManagerService.Injector.

Usually with injectors like these, we are expected to use methods
provided by these instead of directly accessing the fields, so just
returning "null" in Injector.getContext() is counterintuitive and
ideally other callsites which are directly accessing mContext should
be updated to use injector provided one instead.

Bug: 138952436
Test: atest services/tests/servicestests/src/com/android/server/am/ActivityManagerServiceTest.java
Test: atest services/tests/mockingservicestests/src/com/android/server/am/AppCompactorTest.java
Test: atest services/tests/servicestests/src/com/android/server/am/AppErrorDialogTest.java
Change-Id: Idb7cb9a5b7c4c0d237ece9716932a260956a0109
diff --git a/services/tests/servicestests/src/com/android/server/am/AppErrorDialogTest.java b/services/tests/servicestests/src/com/android/server/am/AppErrorDialogTest.java
index 87cc0ff..377bfd1 100644
--- a/services/tests/servicestests/src/com/android/server/am/AppErrorDialogTest.java
+++ b/services/tests/servicestests/src/com/android/server/am/AppErrorDialogTest.java
@@ -51,7 +51,7 @@
     @Before
     public void setUp() throws Exception {
         mContext = getInstrumentation().getTargetContext();
-        mService = new ActivityManagerService(new ActivityManagerService.Injector() {
+        mService = new ActivityManagerService(new ActivityManagerService.Injector(mContext) {
             @Override
             public AppOpsService getAppOpsService(File file, Handler handler) {
                 return null;
@@ -66,11 +66,6 @@
             public boolean isNetworkRestrictedForUid(int uid) {
                 return false;
             }
-
-            @Override
-            public Context getContext() {
-                return mContext;
-            }
         }, mServiceThreadRule.getThread());
         mService.mActivityTaskManager = new ActivityTaskManagerService(mContext);
         mService.mActivityTaskManager.initialize(null, null, mContext.getMainLooper());