Add field trial testing config for app menu icons and regroup

Experiment enabled on canary and dev
https://critique-ng.corp.google.com/cl/330618197

This CL prepares for beta rollout

Change-Id: I21a714b24a6119856963064bb155ab6b421cef45
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2405905Reviewed-by: Theresa  <twellington@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Gang Wu <gangwu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806733}

chrome/android/javatests/src/org/chromium/chrome/browser/app/appmenu/TabbedAppMenuTest.java

@@ -45,6 +45,7 @@ import org.chromium.chrome.test.ChromeJUnit4ClassRunner;
 import org.chromium.chrome.test.ChromeTabbedActivityTestRule;
 import org.chromium.chrome.test.util.ChromeRenderTestRule;
 import org.chromium.chrome.test.util.ChromeTabUtils;
+import org.chromium.chrome.test.util.browser.Features.DisableFeatures;
 import org.chromium.chrome.test.util.browser.Features.EnableFeatures;
 import org.chromium.content_public.browser.UiThreadTaskTraits;
 import org.chromium.content_public.browser.test.util.Criteria;
@@ -242,8 +243,11 @@ public class TabbedAppMenuTest {
     @Test
     @SmallTest
     @Feature({"Browser", "Main", "Bookmark", "RenderTest"})
+    @DisableFeatures({ChromeFeatureList.TABBED_APP_OVERFLOW_MENU_REGROUP,
+            ChromeFeatureList.TABBED_APP_OVERFLOW_MENU_ICONS})
     @DisableIf.Device(type = {UiDisableIf.TABLET}) // See https://crbug.com/1065043.
-    public void testBookmarkMenuItem() throws IOException {
+    public void
+    testBookmarkMenuItem() throws IOException {
         MenuItem bookmarkStar =
                 AppMenuTestSupport.getMenu(mActivityTestRule.getAppMenuCoordinator())
                         .findItem(R.id.bookmark_this_page_id);

testing/variations/fieldtrial_testing_config.json

@@ -87,6 +87,25 @@
             ]
         }
     ],
+    "AndroidAppMenuUiRework": [
+        {
+            "platforms": [
+                "android"
+            ],
+            "experiments": [
+                {
+                    "name": "RegroupBackwardButton",
+                    "params": {
+                        "action_bar": "backward_button"
+                    },
+                    "enable_features": [
+                        "TabbedAppOverflowMenuIcons",
+                        "TabbedAppOverflowMenuRegroup"
+                    ]
+                }
+            ]
+        }
+    ],
     "AndroidDarkSearch": [
         {
             "platforms": [