fix issue #165: leaked GoogleApiClient (#177)

* fix issue #165: leaked GoogleApiClient

* Review feedback

Author: amandle

auth/src/main/java/com/firebase/ui/auth/provider/GoogleProvider.java

@@ -87,6 +87,13 @@ public void setAuthenticationCallback(IDPCallback callback) {
         mIDPCallback = callback;
     }
 
+    public void disconnect() {
+        if (mGoogleApiClient != null) {
+            mGoogleApiClient.disconnect();
+            mGoogleApiClient = null;
+        }
+    }
+
     private IDPResponse createIDPResponse(GoogleSignInAccount account) {
         Bundle response = new Bundle();
         response.putString(TOKEN_KEY, account.getIdToken());

auth/src/main/java/com/firebase/ui/auth/ui/idp/AuthMethodPickerActivity.java

@@ -180,6 +180,18 @@ public void onClick(View view) {
         }
     }
 
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+        if (mIdpProviders != null) {
+            for (final IDPProvider provider : mIdpProviders) {
+                if (provider instanceof GoogleProvider) {
+                    ((GoogleProvider) provider).disconnect();
+                }
+            }
+        }
+    }
+
     public static Intent createIntent(
             Context context,
             FlowParameters flowParams) {