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..e3a5940778cef4f453574c9d539cc6b8c15f66d4
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/sync/SyncAccountSwitcher.java
@@ -0,0 +1,111 @@
+// 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.FragmentManager;
+import android.content.Context;
+import android.preference.Preference;
+import android.preference.Preference.OnPreferenceChangeListener;
+import android.text.TextUtils;
+
+import org.chromium.chrome.browser.BrowsingDataType;
+import org.chromium.chrome.browser.ChromeBrowserProviderClient;
+import org.chromium.chrome.browser.preferences.PrefServiceBridge;
+import org.chromium.chrome.browser.preferences.PrefServiceBridge.OnClearBrowsingDataListener;
+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.ConfirmImportSyncDataFragment;
+
+/**
+ * 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 ConfirmImportSyncDataFragment.Listener#onDialogCompleted}
+ *   {@link OnClearBrowsingDataListener#OnClearBrowsingDataListener}
+ *       (if the user chooses to merge their data, this step is skipped)
+ *   {@link SignInCallback#onSignInComplete}
+ */
+public class SyncAccountSwitcher
+        implements OnPreferenceChangeListener, ConfirmImportSyncDataFragment.Listener,
+                   OnClearBrowsingDataListener, SignInCallback {
+    private static final String TAG = "SyncAccountSwitcher";
+
+    private static final String CONFIRM_IMPORT_SYNC_DATA_DIALOG_TAG =
+            "confirm_import_sync_data_tag";
+
+    private static final int[] SYNC_DATA_TYPES = {
+            BrowsingDataType.HISTORY,
+            BrowsingDataType.CACHE,
+            BrowsingDataType.COOKIES,
+            BrowsingDataType.PASSWORDS,
+            BrowsingDataType.FORM_DATA
+    };
+
+    private final SyncedAccountPreference mSyncedAccountPreference;
+    private final Context mContext;
+    private final FragmentManager mFragmentManager;
+
+    private String mNewAccountName;
+
+    public SyncAccountSwitcher(Context c, FragmentManager fm, SyncedAccountPreference pref) {
+        mSyncedAccountPreference = pref;
+        mContext = c;
+        mFragmentManager = fm;
+    }
+
+    @Override
+    public boolean onPreferenceChange(Preference p, Object newValue) {
+        if (newValue == null) return false;
+
+        SyncedAccountPreference preference = (SyncedAccountPreference) p;
+        mNewAccountName = preference.valueToEntry((String) newValue);
+        String currentAccount = preference.getEntry().toString();
+
+        if (TextUtils.equals(mNewAccountName, currentAccount)) return false;
+
+        ConfirmImportSyncDataFragment confirmSync =
+                ConfirmImportSyncDataFragment.newInstance(currentAccount, mNewAccountName);
+        confirmSync.setListener(this);
+        confirmSync.show(mFragmentManager, CONFIRM_IMPORT_SYNC_DATA_DIALOG_TAG);
+
+        // 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 onDialogCompleted(boolean mergeData) {
+        if (!mergeData) {
+            ChromeBrowserProviderClient.removeAllUserBookmarks(mContext);
+            PrefServiceBridge.getInstance().clearBrowsingData(this, SYNC_DATA_TYPES);

[May, 2016/02/17 14:22:11]

Don't you still need to sign in the new account at this point?

[PEConn, 2016/02/17 17:16:48]

Yes, but not before the browsing data has been cleared. So we have to go through
yet another callback to 'onBrowsingDataCleared' below.

+        } else {
+            signin();
+        }
+    }
+
+    @Override
+    public void onBrowsingDataCleared() {
+        signin();
+    }
+
+    private void signin() {
+        assert mNewAccountName != null;
+        SigninManager.get(mContext).signIn(mNewAccountName, null, this);
+    }
+
+    @Override
+    public void onSignInComplete() {
+        // Update the Preference so it displays the correct account name.
+        mSyncedAccountPreference.update();
+    }
+
+    @Override
+    public void onSignInAborted() {
+        assert false : "Should not be able to abort sign in when switching sync accounts.";
+    }
+}