Enable strict mode to detect leaks of SQLite objects (#386)

In particular this will detect leaked Cursors.

Author: wilhuff

firebase-firestore/src/androidTest/java/com/google/firebase/firestore/testutil/IntegrationTestUtil.java

@@ -21,6 +21,7 @@
 
 import android.content.Context;
 import android.net.SSLCertificateSocketFactory;
+import android.os.StrictMode;
 import android.support.test.InstrumentationRegistry;
 import com.google.android.gms.tasks.Task;
 import com.google.android.gms.tasks.TaskCompletionSource;
@@ -84,6 +85,7 @@ public class IntegrationTestUtil {
 
   private static final FirestoreProvider provider = new FirestoreProvider();
 
+  private static boolean strictModeEnabled = false;
   private static boolean backendPrimed = false;
 
   public static FirestoreProvider provider() {
@@ -202,6 +204,27 @@ public static FirebaseFirestore testAlternateFirestore() {
     return testFirestore(BAD_PROJECT_ID, Level.DEBUG, newTestSettings());
   }
 
+  /**
+   * Enable strict mode for integration tests. Currently checks for leaked SQLite or other Closeable
+   * objects.
+   *
+   * <p>If a leak is found, Android will log the leak and kill the test.
+   */
+  private static void ensureStrictMode() {
+    if (strictModeEnabled) {
+      return;
+    }
+
+    strictModeEnabled = true;
+    StrictMode.setVmPolicy(
+        new StrictMode.VmPolicy.Builder()
+            .detectLeakedSqlLiteObjects()
+            .detectLeakedClosableObjects()
+            .penaltyLog()
+            .penaltyDeath()
+            .build());
+  }
+
   private static void clearPersistence(
       Context context, DatabaseId databaseId, String persistenceKey) {
     @SuppressWarnings("VisibleForTests")
@@ -228,6 +251,7 @@ public static FirebaseFirestore testFirestore(
     DatabaseId databaseId = DatabaseId.forDatabase(projectId, DatabaseId.DEFAULT_DATABASE_ID);
     String persistenceKey = "db" + firestoreStatus.size();
 
+    ensureStrictMode();
     clearPersistence(context, databaseId, persistenceKey);
 
     AsyncQueue asyncQueue = null;