Create a Promise class to simplify dealing with async results.

chrome/android/java/src/org/chromium/chrome/browser/sync/SyncAccountSwitcher.java

Index: chrome/android/java/src/org/chromium/chrome/browser/sync/SyncAccountSwitcher.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/sync/SyncAccountSwitcher.java b/chrome/android/java/src/org/chromium/chrome/browser/sync/SyncAccountSwitcher.java
index 10c5ebf756abeb35131d2d3f01f5fc4620017ec5..0741b716e9cc1ac396fe1fbcb28683bd99105710 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/sync/SyncAccountSwitcher.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/sync/SyncAccountSwitcher.java
@@ -9,6 +9,8 @@ import android.preference.Preference;
 import android.preference.Preference.OnPreferenceChangeListener;
 import android.text.TextUtils;
 
+import org.chromium.base.Callback;
+import org.chromium.base.Promise;
 import org.chromium.chrome.browser.preferences.SyncedAccountPreference;
 import org.chromium.chrome.browser.signin.SigninManager;
 import org.chromium.chrome.browser.signin.SigninManager.SignInCallback;
@@ -74,17 +76,17 @@ public class SyncAccountSwitcher
             public void run() {
                 SigninManager.get(mActivity).clearLastSignedInUser();
 
-                if (wipeData) {
-                    SyncUserDataWiper.wipeSyncUserData(new Runnable() {
-                        @Override
-                        public void run() {
-                            SigninManager.get(mActivity)
-                                    .signIn(mNewAccountName, mActivity, callback);
-                        }
-                    });
-                } else {
-                    SigninManager.get(mActivity).signIn(mNewAccountName, mActivity, callback);
-                }
+                Promise<Void> promise = (wipeData
+                        ? SyncUserDataWiper.wipeSyncUserData()
+                        : Promise.fulfilled((Void) null));
+
+                promise.then(new Callback<Void>(){
+                    @Override
+                    public void onResult(Void result) {
+                        SigninManager.get(mActivity).signIn(mNewAccountName, mActivity, callback);
+
+                    }
+                });
             }
         });
     }