Log exceptions when getting OAuth token

Possibly these should also be fed into `mHandler.onOAuthFailure()`, but
for the moment let's at least log them.

Author: puf

library/src/main/java/com/firebase/ui/auth/google/GoogleOAuthTask.java

@@ -4,6 +4,7 @@
 import android.content.Context;
 import android.content.Intent;
 import android.os.AsyncTask;
+import android.util.Log;
 
 import com.firebase.ui.auth.core.FirebaseLoginError;
 import com.firebase.ui.auth.core.FirebaseResponse;
@@ -12,6 +13,8 @@
 import com.google.android.gms.auth.UserRecoverableAuthException;
 
 class GoogleOAuthTask extends AsyncTask<String, Integer, String> {
+    private final String TAG = "GoogleOAuthTask";
+
     private Context mContext;
     private GoogleOAuthTaskHandler mHandler;
 
@@ -21,11 +24,11 @@ protected String doInBackground(String... emails) {
         try {
             token = GoogleAuthUtil.getToken(mContext, emails[0], "oauth2:profile email");
         } catch (UserRecoverableAuthException e) {
-
+            Log.e(TAG, "Error getting token", e);
         } catch (GoogleAuthException e) {
-
+            Log.e(TAG, "Error getting token", e);
         } catch (java.io.IOException e) {
-
+            Log.e(TAG, "Error getting token", e);
         }
         if (!token.equals("")) return token;
         else return "";