InputMethodSystemServerTests: Make more robust

Spying directly on the Context causes real invocations from the framework
to interfere with the stubbing.

Instead, we create our own spied-on copy of the Context.

Change-Id: I108d60389bc4d8a9c5a007cfb63e8a56093cae45
Test: atest InputMethodSystemServerTests
diff --git a/services/tests/InputMethodSystemServerTests/src/com/android/server/inputmethod/InputMethodManagerServiceTestBase.java b/services/tests/InputMethodSystemServerTests/src/com/android/server/inputmethod/InputMethodManagerServiceTestBase.java
index 1a8e00c..0ed863e 100644
--- a/services/tests/InputMethodSystemServerTests/src/com/android/server/inputmethod/InputMethodManagerServiceTestBase.java
+++ b/services/tests/InputMethodSystemServerTests/src/com/android/server/inputmethod/InputMethodManagerServiceTestBase.java
@@ -19,6 +19,7 @@
 import static com.android.dx.mockito.inline.extended.ExtendedMockito.doNothing;
 import static com.android.dx.mockito.inline.extended.ExtendedMockito.doReturn;
 import static com.android.dx.mockito.inline.extended.ExtendedMockito.mockitoSession;
+import static com.android.dx.mockito.inline.extended.ExtendedMockito.spy;
 import static com.android.dx.mockito.inline.extended.ExtendedMockito.spyOn;
 
 import static org.mockito.ArgumentMatchers.any;
@@ -145,8 +146,7 @@
                         .mockStatic(SystemServerInitThreadPool.class)
                         .startMocking();
 
-        mContext = InstrumentationRegistry.getInstrumentation().getContext();
-        spyOn(mContext);
+        mContext = spy(InstrumentationRegistry.getInstrumentation().getContext());
 
         mTargetSdkVersion = mContext.getApplicationInfo().targetSdkVersion;
         mIsLargeScreen = mContext.getResources().getConfiguration()