Add GPayAppDynamicUpdate feature flag.

The feature flag controls the GPay native app integration for dynamic update with web payments on Android.
The integration for dynamic update is mainly about adding callback service to notify the browser about changes like shipping address.
Design doc is go/dynamic-update-mweb.

Bug: 1074423
Change-Id: I608ca5ddd5aa28f2da5672da83eefd0128720992
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2617201
Commit-Queue: Kaiyu Chen <kylechenkyc@google.com>
Reviewed-by: Sahel Sharify <sahel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841632}

chrome/browser/flags/android/chrome_feature_list.cc

@@ -182,6 +182,7 @@ const base::Feature* kFeaturesExposedToJava[] = {
     &kEphemeralTabUsingBottomSheet,
     &kExploreSites,
     &kFocusOmniboxInIncognitoTabIntents,
+    &kGPayAppDynamicUpdate,
     &kHandleMediaIntents,
     &kHomepagePromoCard,
     &kHorizontalTabSwitcherAndroid,
@@ -508,6 +509,9 @@ const base::Feature kEphemeralTabUsingBottomSheet{
 const base::Feature kExploreSites{"ExploreSites",
                                   base::FEATURE_DISABLED_BY_DEFAULT};
 
+const base::Feature kGPayAppDynamicUpdate{"GPayAppDynamicUpdate",
+                                          base::FEATURE_DISABLED_BY_DEFAULT};
+
 const base::Feature kHandleMediaIntents{"HandleMediaIntents",
                                         base::FEATURE_ENABLED_BY_DEFAULT};
 

chrome/browser/flags/android/chrome_feature_list.h

@@ -79,6 +79,7 @@ extern const base::Feature kEnhancedProtectionPromoCard;
 extern const base::Feature kEphemeralTabUsingBottomSheet;
 extern const base::Feature kExploreSites;
 extern const base::Feature kFocusOmniboxInIncognitoTabIntents;
+extern const base::Feature kGPayAppDynamicUpdate;
 extern const base::Feature kHandleMediaIntents;
 extern const base::Feature kHomepagePromoCard;
 extern const base::Feature kHorizontalTabSwitcherAndroid;

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

@@ -316,6 +316,7 @@ public abstract class ChromeFeatureList {
     public static final String FILLING_PASSWORDS_FROM_ANY_ORIGIN = "FillingPasswordsFromAnyOrigin";
     public static final String FOCUS_OMNIBOX_IN_INCOGNITO_TAB_INTENTS =
             "FocusOmniboxInIncognitoTabIntents";
+    public static final String GPAY_APP_DYNAMIC_UPDATE = "GPayAppDynamicUpdate";
     public static final String GRANT_NOTIFICATIONS_TO_DSE = "GrantNotificationsToDSE";
     public static final String HANDLE_MEDIA_INTENTS = "HandleMediaIntents";
     public static final String HIDE_FROM_API_3_TRANSITIONS_FROM_HISTORY =