Remove toolbar progress bar on start surface home page.

Bug: 1136599
Change-Id: If780a0d396724dd3551987534cfdacce27cc8f1e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2482202
Commit-Queue: Hao Dong <spdonghao@chromium.org>
Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Reviewed-by: Matthew Jones <mdjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#818509}

chrome/android/java/src/org/chromium/chrome/browser/toolbar/load_progress/LoadProgressMediator.java

@@ -10,6 +10,7 @@ import org.chromium.chrome.browser.native_page.NativePageFactory;
 import org.chromium.chrome.browser.tab.EmptyTabObserver;
 import org.chromium.chrome.browser.tab.Tab;
 import org.chromium.chrome.browser.toolbar.load_progress.LoadProgressProperties.CompletionState;
+import org.chromium.chrome.features.start_surface.StartSurfaceConfiguration;
 import org.chromium.components.embedder_support.util.UrlUtilities;
 import org.chromium.content_public.browser.NavigationHandle;
 import org.chromium.ui.modelutil.PropertyModel;
@@ -111,7 +112,14 @@ public class LoadProgressMediator {
     }
 
     private void onNewTabObserved(Tab tab) {
-        if (tab == null) return;
+        if (tab == null) {
+            // If start surface is enabled and new tab is null, then new tab is home page or tab
+            // switcher. Finish progress bar loading.
+            if (StartSurfaceConfiguration.isStartSurfaceEnabled()) {
+                finishLoadProgress(false);
+            }
+            return;
+        }
 
         if (tab.isLoading()) {
             if (NativePageFactory.isNativePageUrl(tab.getUrlString(), tab.isIncognito())) {