Created the dialog offering the user to merge their account data or keep it

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
new file mode 100644
index 0000000000000000000000000000000000000000..bb70a3f233194fae703449a029e7cb5bcac771ed
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/sync/SyncAccountSwitcher.java
@@ -0,0 +1,81 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.chrome.browser.sync;
+
+import android.app.Activity;
+import android.preference.Preference;
+import android.preference.Preference.OnPreferenceChangeListener;
+import android.text.TextUtils;
+
+import org.chromium.chrome.browser.preferences.SyncedAccountPreference;
+import org.chromium.chrome.browser.signin.SigninManager;
+import org.chromium.chrome.browser.signin.SigninManager.SignInCallback;
+import org.chromium.chrome.browser.sync.ui.ConfirmImportSyncDataDialog;
+import org.chromium.chrome.browser.sync.ui.ConfirmImportSyncDataDialog.ImportSyncType;
+
+/**
+ * A class that encapsulates the control flow of listeners and callbacks when switching sync
+ * accounts.
+ *
+ * Control flows through the method in this order:
+ *   {@link OnPreferenceChangeListener#onPreferenceChange}
+ *   {@link ConfirmImportSyncDataDialog.Listener#onConfirm}
+ *   {@link SignInCallback#onSignInComplete}
+ */
+public class SyncAccountSwitcher
+        implements OnPreferenceChangeListener, ConfirmImportSyncDataDialog.Listener,
+                   SignInCallback {
+    private static final String TAG = "SyncAccountSwitcher";
+
+    private final SyncedAccountPreference mSyncedAccountPreference;
+    private final Activity mActivity;
+
+    private String mNewAccountName;
+
+    /**
+     * Sets up a SyncAccountSwitcher to be ready to accept callbacks.
+     * @param activity Activity used to get the context for signin and get the fragmentManager
+     *                 for the data sync fragment.
+     * @param syncedAccountPreference The preference to update once signin has been completed.
+     */
+    public SyncAccountSwitcher(Activity activity, SyncedAccountPreference syncedAccountPreference) {
+        mActivity = activity;
+        mSyncedAccountPreference = syncedAccountPreference;
+    }
+
+    @Override
+    public boolean onPreferenceChange(Preference p, Object newValue) {
+        if (newValue == null) return false;
+
+        mNewAccountName = (String) newValue;
+        String currentAccount = mSyncedAccountPreference.getValue();
+
+        if (TextUtils.equals(mNewAccountName, currentAccount)) return false;
+
+        ConfirmImportSyncDataDialog.showNewInstance(currentAccount, mNewAccountName,
+                ImportSyncType.SWITCHING_SYNC_ACCOUNTS, mActivity.getFragmentManager(), this);
+
+        // Don't update the selected account in the preference. It will be updated by
+        // the call to mSyncAccountListPreference.update() if everything succeeds.
+        return false;
+    }
+
+    @Override
+    public void onConfirm() {
+        assert mNewAccountName != null;
+        SigninManager.get(mActivity).signIn(mNewAccountName, mActivity, this);
+    }
+
+    @Override
+    public void onSignInComplete() {
+        // Update the Preference so it displays the correct account name.
+        mSyncedAccountPreference.update();
+    }
+
+    @Override
+    public void onSignInAborted() {
+        // If the user aborted signin, there is nothing to do.
+    }
+}