[PaymentHandler] Open a blank PaymentHandler bottom-sheet behind a flag

The PaymentHandler UI is opened as an ChromeCustomTab Activity. Going
forwards, we will refactor the Payment Handler to make it based on
bottom-sheet.

For this purpose, this CL adds:
* A blank bottom-sheet-based Payment Handler UI.
* "ScrollToExpandPaymentHandler" to enable the incomplete feature while
we are still developing the refactored solution.

Here's the expected change after the patch:

Flag:
When this flag is disabled (default), Payment Handler is unchanged.
When this flag is enabled (--enable-features=ScrollToExpandPaymentHandler),
the Payment Handler UI is changed to blank widget.

The Payment Handler bottom-sheet:
The Payment Handler UI will be displayed as an empty bottom-sheet. The
swipe-down can dismissing the UI; the swipe-up can maximize the UI.

Bug: 999196

Change-Id: Id839dfe63a9473243c5864295c5ae435ee725e55
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1832702
Commit-Queue: Liquan (Max) Gu <maxlg@chromium.org>
Reviewed-by: Rouslan Solomakhin <rouslan@chromium.org>
Reviewed-by: Matthew Jones <mdjones@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#702998}

chrome/android/chrome_java_sources.gni

@@ -1199,6 +1199,11 @@ chrome_java_sources = [
   "java/src/org/chromium/chrome/browser/payments/CanMakePaymentQuery.java",
   "java/src/org/chromium/chrome/browser/payments/CardEditor.java",
   "java/src/org/chromium/chrome/browser/payments/ContactEditor.java",
+  "java/src/org/chromium/chrome/browser/payments/handler/PaymentHandlerCoordinator.java",
+  "java/src/org/chromium/chrome/browser/payments/handler/PaymentHandlerMediator.java",
+  "java/src/org/chromium/chrome/browser/payments/handler/PaymentHandlerProperties.java",
+  "java/src/org/chromium/chrome/browser/payments/handler/PaymentHandlerViewBinder.java",
+  "java/src/org/chromium/chrome/browser/payments/handler/PaymentHandlerView.java",
   "java/src/org/chromium/chrome/browser/payments/JourneyLogger.java",
   "java/src/org/chromium/chrome/browser/payments/PackageManagerDelegate.java",
   "java/src/org/chromium/chrome/browser/payments/PaymentApp.java",

chrome/android/java/res/layout/payment_handler_content.xml

+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright 2019 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. -->
+<RelativeLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:background="@color/sheet_bg_color"
+    android:layout_height="match_parent"
+    android:layout_width="match_parent">
+</RelativeLayout>

chrome/android/java/res/layout/payment_handler_toolbar.xml

+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright 2019 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. -->
+<RelativeLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content">
+</RelativeLayout>

chrome/android/java/src/org/chromium/chrome/browser/ChromeFeatureList.java

@@ -312,6 +312,7 @@ public abstract class ChromeFeatureList {
     public static final String REMOVE_NAVIGATION_HISTORY = "RemoveNavigationHistory";
     public static final String REORDER_BOOKMARKS = "ReorderBookmarks";
     public static final String REVAMPED_CONTEXT_MENU = "RevampedContextMenu";
+    public static final String SCROLL_TO_EXPAND_PAYMENT_HANDLER = "ScrollToExpandPaymentHandler";
     public static final String SEND_TAB_TO_SELF = "SyncSendTabToSelf";
     public static final String SERVICE_MANAGER_FOR_DOWNLOAD = "ServiceManagerForDownload";
     public static final String SERVICE_WORKER_PAYMENT_APPS = "ServiceWorkerPaymentApps";

chrome/android/java/src/org/chromium/chrome/browser/ServiceTabLauncher.java

@@ -23,6 +23,8 @@ import org.chromium.chrome.R;
 import org.chromium.chrome.browser.browserservices.BrowserServicesMetrics;
 import org.chromium.chrome.browser.browserservices.TrustedWebActivityClient;
 import org.chromium.chrome.browser.customtabs.CustomTabIntentDataProvider;
+import org.chromium.chrome.browser.payments.PaymentRequestImpl;
+import org.chromium.chrome.browser.payments.handler.PaymentHandlerCoordinator;
 import org.chromium.chrome.browser.tab.Tab;
 import org.chromium.chrome.browser.tabmodel.TabLaunchType;
 import org.chromium.chrome.browser.tabmodel.document.AsyncTabCreationParams;
@@ -41,6 +43,8 @@ import org.chromium.webapk.lib.client.WebApkIdentityServiceClient;
 import org.chromium.webapk.lib.client.WebApkNavigationClient;
 import org.chromium.webapk.lib.client.WebApkValidator;
 
+import java.net.URI;
+import java.net.URISyntaxException;
 import java.util.List;
 
 /**
@@ -75,7 +79,14 @@ public class ServiceTabLauncher {
         // Open popup window in custom tab.
         // Note that this is used by PaymentRequestEvent.openWindow().
         if (disposition == WindowOpenDisposition.NEW_POPUP) {
-            if (!createPopupCustomTab(requestId, url, incognito)) {
+            boolean success = false;
+            try {
+                success = PaymentHandlerCoordinator.isEnabled()
+                        ? PaymentRequestImpl.openPaymentHandlerWindow(new URI(url))
+                        : createPopupCustomTab(requestId, url, incognito);
+            } catch (URISyntaxException e) { /* Intentionally leave blank, so success is false. */
+            }
+            if (!success) {
                 PostTask.postTask(UiThreadTaskTraits.DEFAULT,
                         () -> onWebContentsForRequestAvailable(requestId, null));
             }

chrome/android/java/src/org/chromium/chrome/browser/payments/PaymentRequestImpl.java

@@ -23,11 +23,13 @@ import org.chromium.chrome.browser.autofill.PersonalDataManager;
 import org.chromium.chrome.browser.autofill.PersonalDataManager.AutofillProfile;
 import org.chromium.chrome.browser.autofill.PersonalDataManager.CreditCard;
 import org.chromium.chrome.browser.autofill.PersonalDataManager.NormalizedAddressRequestDelegate;
+import org.chromium.chrome.browser.browserservices.Origin;
 import org.chromium.chrome.browser.compositor.layouts.EmptyOverviewModeObserver;
 import org.chromium.chrome.browser.compositor.layouts.OverviewModeBehavior;
 import org.chromium.chrome.browser.compositor.layouts.OverviewModeBehavior.OverviewModeObserver;
 import org.chromium.chrome.browser.favicon.FaviconHelper;
 import org.chromium.chrome.browser.page_info.CertificateChainHelper;
+import org.chromium.chrome.browser.payments.handler.PaymentHandlerCoordinator;
 import org.chromium.chrome.browser.payments.micro.MicrotransactionCoordinator;
 import org.chromium.chrome.browser.payments.ui.ContactDetailsSection;
 import org.chromium.chrome.browser.payments.ui.LineItem;
@@ -268,10 +270,10 @@ public class PaymentRequestImpl
     private static boolean sIsLocalCanMakePaymentQueryQuotaEnforcedForTest;
 
     /**
-     * True if show() was called in any PaymentRequestImpl object. Used to prevent showing more than
-     * one PaymentRequest UI per browser process.
+     * Hold the currently showing PaymentRequest. Used to prevent showing more than one
+     * PaymentRequest UI per browser process.
      */
-    private static boolean sIsAnyPaymentRequestShowing;
+    private static PaymentRequestImpl sShowingPaymentRequest;
 
     /** Monitors changes in the TabModelSelector. */
     private final TabModelSelectorObserver mSelectorObserver = new EmptyTabModelSelectorObserver() {
@@ -376,6 +378,7 @@ public class PaymentRequestImpl
     private MicrotransactionCoordinator mMicrotransactionUi;
     private Callback<PaymentInformation> mPaymentInformationCallback;
     private PaymentInstrument mInvokedPaymentInstrument;
+    private PaymentHandlerCoordinator mPaymentHandlerUi;
     private boolean mMerchantSupportsAutofillPaymentInstruments;
     private boolean mUserCanAddCreditCard;
     private boolean mHideServerAutofillInstruments;
@@ -721,7 +724,7 @@ public class PaymentRequestImpl
                     activity, mAutofillProfiles, mContactEditor, mJourneyLogger);
         }
 
-        setIsAnyPaymentRequestShowing(true);
+        setShowingPaymentRequest(this);
         mUI = new PaymentRequestUI(activity, this, mRequestShipping,
                 /* requestShippingOption= */ mRequestShipping,
                 mRequestPayerName || mRequestPayerPhone || mRequestPayerEmail,
@@ -865,6 +868,21 @@ public class PaymentRequestImpl
         triggerPaymentAppUiSkipIfApplicable(chromeActivity);
     }
 
+    private void dimBackgroundIfNotBottomSheetPaymentHandler(PaymentInstrument selectedInstrument) {
+        // Putting isEnabled() last is intentional. It's to ensure not to confused the unexecuted
+        // group and the disabled in A/B testing.
+        if ((selectedInstrument instanceof ServiceWorkerPaymentApp)
+                && PaymentHandlerCoordinator.isEnabled()) {
+            // When the Payment Handler (PH) UI is based on Activity, dimming the Payment
+            // Request (PR) UI does not dim the PH; when it's based on bottom-sheet, dimming
+            // the PR dims both UIs. As bottom-sheet itself has dimming effect, dimming PR
+            // is unnecessary for the bottom-sheet PH. For now, ServiceWorkerPaymentApp is the only
+            // payment app that can open the bottom-sheet.
+            return;
+        }
+        mUI.dimBackground();
+    }
+
     private void triggerPaymentAppUiSkipIfApplicable(ChromeActivity chromeActivity) {
         // If we are skipping showing the Payment Request UI, we should call into the
         // PaymentApp immediately after we determine the instruments are ready and UI is shown.
@@ -891,7 +909,7 @@ public class PaymentRequestImpl
                             && !mIsUserGestureShow)) {
                 mUI.show();
             } else {
-                mUI.dimBackground();
+                dimBackgroundIfNotBottomSheetPaymentHandler(selectedInstrument);
                 mDidRecordShowEvent = true;
                 mShouldRecordAbortReason = true;
                 mJourneyLogger.setEventOccurred(Event.SKIPPED_SHOW);
@@ -934,7 +952,7 @@ public class PaymentRequestImpl
                     mCurrencyFormatterMap.get(mRawTotal.amount.currency),
                     mUiShoppingCart.getTotal(), this::onMicrotransactionUiConfirmed,
                     this::onMicrotransactionUiDismissed)) {
-            setIsAnyPaymentRequestShowing(true);
+            setShowingPaymentRequest(this);
             mDidRecordShowEvent = true;
             mShouldRecordAbortReason = true;
             mJourneyLogger.setEventOccurred(Event.SHOWN);
@@ -1143,6 +1161,41 @@ public class PaymentRequestImpl
         return changePaymentMethodFromInvokedApp(methodName, stringifiedData);
     }
 
+    /**
+     *  Called to open a new PaymentHandler UI on the showing PaymentRequest.
+     *  @param url The url of the payment app to be displayed in the UI.
+     *  @return Whether the opening is successful.
+     */
+    public static boolean openPaymentHandlerWindow(URI url) {
+        return sShowingPaymentRequest != null
+                && sShowingPaymentRequest.openPaymentHandlerWindowInternal(url);
+    }
+
+    /**
+     *  Called to open a new PaymentHandler UI on this PaymentRequest.
+     *  @param url The url of the payment app to be displayed in the UI.
+     *  @return Whether the opening is successful.
+     */
+    private boolean openPaymentHandlerWindowInternal(URI url) {
+        assert mInvokedPaymentInstrument != null;
+        assert mInvokedPaymentInstrument instanceof ServiceWorkerPaymentApp;
+        assert new Origin(url.toString())
+                .equals(new Origin(((ServiceWorkerPaymentApp) mInvokedPaymentInstrument)
+                                           .getScope()
+                                           .toString()));
+
+        if (mPaymentHandlerUi != null) return false;
+        mPaymentHandlerUi = new PaymentHandlerCoordinator();
+        ChromeActivity chromeActivity = ChromeActivity.fromWebContents(mWebContents);
+        if (chromeActivity == null) return false;
+        return mPaymentHandlerUi.show(chromeActivity, this::onPaymentHandlerUiDismissed);
+    }
+
+    private void onPaymentHandlerUiDismissed() {
+        ensureHideAndResetPaymentHandlerUi();
+        ServiceWorkerPaymentAppBridge.onClosingPaymentAppWindow(mWebContents);
+    }
+
     @Override
     public boolean isInvokedInstrumentValidForPaymentMethodIdentifier(String methodName) {
         return mInvokedPaymentInstrument != null
@@ -2531,6 +2584,12 @@ public class PaymentRequestImpl
         PersonalDataManager.getInstance().normalizeAddress(address.getProfile(), this);
     }
 
+    private void ensureHideAndResetPaymentHandlerUi() {
+        if (mPaymentHandlerUi == null) return;
+        mPaymentHandlerUi.hide();
+        mPaymentHandlerUi = null;
+    }
+
     /**
      * Closes the UI and destroys native objects. If the client is still connected, then it's
      * notified of UI hiding. This PaymentRequestImpl object can't be reused after this function is
@@ -2545,10 +2604,11 @@ public class PaymentRequestImpl
      *                       always pass "true."
      */
     private void closeUIAndDestroyNativeObjects(boolean immediateClose) {
+        ensureHideAndResetPaymentHandlerUi();
         if (mMicrotransactionUi != null) {
             mMicrotransactionUi.hide();
             mMicrotransactionUi = null;
-            setIsAnyPaymentRequestShowing(false);
+            setShowingPaymentRequest(null);
         }
 
         if (mUI != null) {
@@ -2560,7 +2620,7 @@ public class PaymentRequestImpl
                 closeClient();
             });
             mUI = null;
-            setIsAnyPaymentRequestShowing(false);
+            setShowingPaymentRequest(null);
         }
 
         mIsCurrentPaymentRequestShowing = false;
@@ -2612,16 +2672,18 @@ public class PaymentRequestImpl
     }
 
     /**
-     * @return Whether any instance of PaymentRequest has received a show() call. Don't use this
-     *         function to check whether the current instance has received a show() call.
+     * @return Whether any instance of PaymentRequest has received a show() call.
+     *         Don't use this function to check whether the current instance has
+     *         received a show() call.
      */
     private static boolean getIsAnyPaymentRequestShowing() {
-        return sIsAnyPaymentRequestShowing;
+        return sShowingPaymentRequest != null;
     }
 
-    /** @param isShowing Whether any instance of PaymentRequest has received a show() call. */
-    private static void setIsAnyPaymentRequestShowing(boolean isShowing) {
-        sIsAnyPaymentRequestShowing = isShowing;
+    /** @param paymentRequest The currently showing PaymentRequestImpl. */
+    private static void setShowingPaymentRequest(PaymentRequestImpl paymentRequest) {
+        assert sShowingPaymentRequest == null || paymentRequest == null;
+        sShowingPaymentRequest = paymentRequest;
     }
 
     @VisibleForTesting

chrome/android/java/src/org/chromium/chrome/browser/payments/ServiceWorkerPaymentApp.java

@@ -214,6 +214,10 @@ public class ServiceWorkerPaymentApp extends PaymentInstrument implements Paymen
         mPaymentHandlerHost = host;
     }
 
+    /*package*/ URI getScope() {
+        return mScope;
+    }
+
     @Override
     public void getInstruments(String id, Map<String, PaymentMethodData> methodDataMap,
             String origin, String iframeOrigin, byte[][] unusedCertificateChain,

chrome/android/java/src/org/chromium/chrome/browser/payments/handler/PaymentHandlerCoordinator.java

+// Copyright 2019 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.payments.handler;
+
+import org.chromium.chrome.browser.ChromeActivity;
+import org.chromium.chrome.browser.ChromeFeatureList;
+import org.chromium.chrome.browser.widget.bottomsheet.BottomSheetController;
+import org.chromium.ui.modelutil.PropertyModel;
+import org.chromium.ui.modelutil.PropertyModelChangeProcessor;
+
+/**
+ * PaymentHandler coordinator, which owns the component overall, i.e., creates other objects in the
+ * component and connects them. It decouples the implementation of this component from other
+ * components and acts as the point of contact between them. Any code in this component that needs
+ * to interact with another component does that through this coordinator.
+ */
+public class PaymentHandlerCoordinator {
+    private Runnable mHider;
+
+    /** Observer for the dismissal of the payment-handler UI. */
+    public interface DismissObserver {
+        /**
+         * Called after the user has dismissed the payment-handler UI by swiping it down or tapping
+         * on the scrim behind the UI.
+         */
+        void onDismissed();
+    }
+
+    /** Constructs the payment-handler component coordinator. */
+    public PaymentHandlerCoordinator() {
+        assert isEnabled();
+    }
+
+    /**
+     * Shows the payment-handler UI.
+     *
+     * @param chromeActivity  The activity where the UI should be shown.
+     * @param dismissObserver The observer to be notified when the user has dismissed the UI.
+     * @return Whether the payment-handler UI was shown. Can be false if the UI was suppressed.
+     */
+    public boolean show(ChromeActivity activity, DismissObserver dismissObserver) {
+        assert mHider == null : "Already showing payment-handler UI";
+        PaymentHandlerMediator mediator = new PaymentHandlerMediator(this::hide, dismissObserver);
+        BottomSheetController bottomSheetController = activity.getBottomSheetController();
+        bottomSheetController.getBottomSheet().addObserver(mediator);
+        PropertyModel model = new PropertyModel.Builder(PaymentHandlerProperties.ALL_KEYS).build();
+        PaymentHandlerView view = new PaymentHandlerView(activity);
+        PropertyModelChangeProcessor changeProcessor =
+                PropertyModelChangeProcessor.create(model, view, PaymentHandlerViewBinder::bind);
+        mHider = () -> {
+            changeProcessor.destroy();
+            bottomSheetController.getBottomSheet().removeObserver(mediator);
+            bottomSheetController.hideContent(/*content=*/view, /*animate=*/true);
+        };
+        boolean result = bottomSheetController.requestShowContent(view, /*animate=*/true);
+        if (result) bottomSheetController.expandSheet();
+        return result;
+    }
+
+    /** Hides the payment-handler UI. */
+    public void hide() {
+        if (mHider == null) return;
+        mHider.run();
+    }
+
+    /**
+     * @return Whether this solution (as opposed to the Chrome-custom-tab based solution) of
+     *     PaymentHandler is enabled. This solution is intended to replace the other
+     *     solution.
+     */
+    public static boolean isEnabled() {
+        return ChromeFeatureList.isEnabled(ChromeFeatureList.SCROLL_TO_EXPAND_PAYMENT_HANDLER);
+    }
+}

chrome/android/java/src/org/chromium/chrome/browser/payments/handler/PaymentHandlerMediator.java

+// Copyright 2019 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.payments.handler;
+
+import org.chromium.chrome.browser.payments.handler.PaymentHandlerCoordinator.DismissObserver;
+import org.chromium.chrome.browser.widget.bottomsheet.BottomSheet.SheetState;
+import org.chromium.chrome.browser.widget.bottomsheet.EmptyBottomSheetObserver;
+
+/**
+ * PaymentHandler mediator, which is responsible for receiving events from the view and notifies the
+ * backend (the coordinator).
+ */
+/* package */ class PaymentHandlerMediator extends EmptyBottomSheetObserver {
+    private final Runnable mHider;
+    private final DismissObserver mDismissObserver;
+
+    /* package */ PaymentHandlerMediator(Runnable hider, DismissObserver dismissObserver) {
+        mHider = hider;
+        mDismissObserver = dismissObserver;
+    }
+
+    // EmptyBottomSheetObserver:
+    @Override
+    public void onSheetStateChanged(@SheetState int newState) {
+        switch (newState) {
+            case SheetState.HIDDEN:
+                mHider.run();
+                mDismissObserver.onDismissed();
+                break;
+        }
+    }
+}

chrome/android/java/src/org/chromium/chrome/browser/payments/handler/PaymentHandlerProperties.java

+// Copyright 2019 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.payments.handler;
+
+import org.chromium.ui.modelutil.PropertyKey;
+
+/** PaymentHandler UI properties, which fully describe the state of the UI. */
+/* package */ class PaymentHandlerProperties {
+    // TODO(maxlg): Should add more keys after we add more states to the widget .
+    /* package */ static final PropertyKey[] ALL_KEYS = new PropertyKey[] {};
+
+    // Prevent instantiation.
+    private PaymentHandlerProperties() {}
+}

chrome/android/java/src/org/chromium/chrome/browser/payments/handler/PaymentHandlerView.java

+// Copyright 2019 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.payments.handler;
+
+import android.content.Context;
+import android.support.annotation.Nullable;
+import android.view.LayoutInflater;
+import android.view.View;
+
+import org.chromium.chrome.R;
+import org.chromium.chrome.browser.widget.bottomsheet.BottomSheet;
+import org.chromium.chrome.browser.widget.bottomsheet.BottomSheet.BottomSheetContent;
+
+/** PaymentHandler UI. */
+/* package */ class PaymentHandlerView implements BottomSheetContent {
+    private final View mToolbarView;
+    private final View mContentView;
+
+    /* package */ PaymentHandlerView(Context context) {
+        mToolbarView = LayoutInflater.from(context).inflate(R.layout.payment_handler_toolbar, null);
+        mContentView = LayoutInflater.from(context).inflate(R.layout.payment_handler_content, null);
+    }
+
+    // BottomSheetContent:
+    @Override
+    public View getContentView() {
+        return mContentView;
+    }
+
+    @Override
+    @Nullable
+    public View getToolbarView() {
+        return mToolbarView;
+    }
+
+    @Override
+    public int getVerticalScrollOffset() {
+        return 0;
+    }
+
+    @Override
+    public void destroy() {}
+
+    @Override
+    @BottomSheet.ContentPriority
+    public int getPriority() {
+        // If multiple bottom sheets are queued up to be shown, prioritize payment-handler, because
+        // it's triggered by a user gesture, such as a click on <button>Buy this article</button>.
+        return BottomSheet.ContentPriority.HIGH;
+    }
+
+    @Override
+    public boolean isPeekStateEnabled() {
+        return false;
+    }
+
+    @Override
+    public boolean wrapContentEnabled() {
+        return false;
+    }
+
+    @Override
+    public int getSheetContentDescriptionStringId() {
+        return R.string.payment_request_payment_method_section_name;
+    }
+
+    @Override
+    public int getSheetHalfHeightAccessibilityStringId() {
+        return R.string.payment_request_payment_method_section_name;
+    }
+
+    @Override
+    public int getSheetFullHeightAccessibilityStringId() {
+        return R.string.payment_request_payment_method_section_name;
+    }
+
+    @Override
+    public int getSheetClosedAccessibilityStringId() {
+        return R.string.payment_request_payment_method_section_name;
+    }
+
+    @Override
+    public boolean swipeToDismissEnabled() {
+        // flinging down hard enough will close the sheet.
+        return true;
+    }
+}

chrome/android/java/src/org/chromium/chrome/browser/payments/handler/PaymentHandlerViewBinder.java

+// Copyright 2019 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.payments.handler;
+
+import org.chromium.ui.modelutil.PropertyKey;
+import org.chromium.ui.modelutil.PropertyModel;
+
+/**
+ * PaymentHandler view binder, which is stateless. It is called to bind a given model to a given
+ * view. Should contain as little business logic as possible.
+ */
+/* package */ class PaymentHandlerViewBinder {
+    /* package */ static void bind(
+            PropertyModel model, PaymentHandlerView view, PropertyKey propertyKey) {
+        // TODO(maxlg): bind model properties to view after adding view widgets.
+    }
+}

chrome/browser/android/chrome_feature_list.cc

@@ -161,6 +161,7 @@ const base::Feature* kFeaturesExposedToJava[] = {
     &kReaderModeInCCT,
     &kReorderBookmarks,
     &kRevampedContextMenu,
+    &kScrollToExpandPaymentHandler,
     &kSearchEnginePromoExistingDevice,
     &kSearchEnginePromoNewDevice,
     &kServiceManagerForBackgroundPrefetch,
@@ -503,6 +504,9 @@ const base::Feature kReorderBookmarks{"ReorderBookmarks",
 const base::Feature kRevampedContextMenu{"RevampedContextMenu",
                                          base::FEATURE_DISABLED_BY_DEFAULT};
 
+const base::Feature kScrollToExpandPaymentHandler{
+    "ScrollToExpandPaymentHandler", base::FEATURE_DISABLED_BY_DEFAULT};
+
 const base::Feature kServiceManagerForBackgroundPrefetch{
     "ServiceManagerForBackgroundPrefetch", base::FEATURE_DISABLED_BY_DEFAULT};
 

chrome/browser/android/chrome_feature_list.h

@@ -96,6 +96,7 @@ extern const base::Feature kReachedCodeProfiler;
 extern const base::Feature kReorderBookmarks;
 extern const base::Feature kReaderModeInCCT;
 extern const base::Feature kRevampedContextMenu;
+extern const base::Feature kScrollToExpandPaymentHandler;
 extern const base::Feature kSearchEnginePromoExistingDevice;
 extern const base::Feature kSearchEnginePromoNewDevice;
 extern const base::Feature kServiceManagerForBackgroundPrefetch;