Fix for failing SecurityPolicyTests.

This fixes the following exception.

java.lang.UnsupportedOperationException
        at android.test.mock.MockContext.getApplicationContext(MockContext.java:82)

Bug 2725552

Change-Id: Iaca177defe5f5e836211c58270379da056fa64e0

tests/src/com/android/email/SecurityPolicyTests.java

@@ -62,7 +62,9 @@ public class SecurityPolicyTests extends ProviderTestCase2<EmailProvider> {
     }
 
     /**
-     * Private context wrapper used to add back getPackageName() for these tests
+     * Private context wrapper used to add back getPackageName() for these tests.
+     *
+     * This class also implements {@link Context} method(s) that is called during tests.
      */
     private static class MockContext2 extends ContextWrapper {
 
@@ -73,6 +75,11 @@ public class SecurityPolicyTests extends ProviderTestCase2<EmailProvider> {
             mRealContext = realContext;
         }
 
+        @Override
+        public Context getApplicationContext() {
+            return this;
+        }
+
         @Override
         public String getPackageName() {
             return mRealContext.getPackageName();