[ExploreSites]: ESP should default to top of the page if variation is MostLikely.

Bug: 971323
Change-Id: Iabdccb8e835bae9b32a2435d6eb31e15ec2aa213
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1646552Reviewed-by: Justin DeWitt <dewittj@chromium.org>
Commit-Queue: Cathy Li <chili@chromium.org>
Cr-Commit-Position: refs/heads/master@{#667320}

chrome/android/java/src/org/chromium/chrome/browser/explore_sites/ExploreSitesPage.java

@@ -182,9 +182,11 @@ public class ExploreSitesPage extends BasicNativePage {
             }
         });
 
-        // When we personalize, we don't want to scroll to the 4th category.
-        mInitialScrollPosition =
-                ExploreSitesBridge.getVariation() == ExploreSitesVariation.PERSONALIZED
+        // We don't want to scroll to the 4th category if personalized
+        // or integrated with Most Likely.
+        int variation = ExploreSitesBridge.getVariation();
+        mInitialScrollPosition = variation == ExploreSitesVariation.PERSONALIZED
+                        || ExploreSitesBridge.isIntegratedWithMostLikely(variation)
                 ? INITIAL_SCROLL_POSITION_PERSONALIZED
                 : INITIAL_SCROLL_POSITION;
 

chrome/android/javatests/src/org/chromium/chrome/browser/explore_sites/ExploreSitesPageTest.java

@@ -140,6 +140,18 @@ public class ExploreSitesPageTest {
         mRenderTestRule.render(mRecyclerView, "initial_layout");
     }
 
+    @Test
+    @SmallTest
+    @CommandLineFlags.
+    Add({"enabled-features=ExploreSites<FakeStudyName", "force-fieldtrials=FakeStudyName/Enabled",
+            "force-fieldtrial-params=FakeStudyName.Enabled:variation/mostLikelyTile"})
+    @Feature({"ExploreSites", "RenderTest"})
+    public void
+    testInitialLayout_MostLikely() throws Exception {
+        mRenderTestRule.render(mRecyclerView, "initial_layout");
+        Assert.assertEquals(0, getFirstVisiblePosition());
+    }
+
     @Test
     @SmallTest
     @Feature({"ExploreSites", "RenderTest"})