[StartTablet] Fix assert error ReturnToChromeUtil.willAddTab.

(cherry picked from commit 2aab169)

Bug: 1450004
Change-Id: I736c2a0a4e7ddad6ce93285dcc120577f432d289
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4574994
Commit-Queue: Xi Han <hanxi@chromium.org>
Reviewed-by: Theresa Sullivan <twellington@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1152024}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4589270
Reviewed-by: Calder Kitagawa <ckitagawa@chromium.org>
Cr-Commit-Position: refs/branch-heads/5790@{#358}
Cr-Branched-From: 1d71a33-refs/heads/main@{#1148114}

chrome/android/java/src/org/chromium/chrome/browser/tasks/ReturnToChromeUtil.java

@@ -587,11 +587,25 @@ public static Tab createNewTabAndShowHomeSurfaceUi(@NonNull TabCreator tabCreato
             TabModelObserver observer = new TabModelObserver() {
                 @Override
                 public void willAddTab(Tab tab, int type) {
-                    assert TextUtils.equals(lastActiveTabUrl, tab.getUrl().getSpec())
-                        : "The URL of first Tab restored doesn't match the URL of the last active Tab read from the Tab state metadata file!";
+                    boolean isTabExpected =
+                            TextUtils.equals(lastActiveTabUrl, tab.getUrl().getSpec());
+                    assert isTabExpected
+                        : "The URL of first Tab restored doesn't match the URL of the last active "
+                          + "Tab read from the Tab state metadata file! Existing Tab count = %d"
+                          + tabModelSelector.getModel(false).getCount()
+                          + ".";
+                    if (!isTabExpected) {
+                        return;
+                    }
                     showHomeSurfaceUiOnNtp(ntpTab, tab, homeSurfaceTracker);
                     tabModelSelector.getModel(false).removeObserver(this);
                 }
+
+                @Override
+                public void restoreCompleted() {
+                    // This would be no-op if the observer has been removed in willAddTab().
+                    tabModelSelector.getModel(false).removeObserver(this);
+                }
             };
             tabModelSelector.getModel(false).addObserver(observer);
         } else {

chrome/android/junit/src/org/chromium/chrome/browser/tasks/ReturnToChromeUtilUnitTest.java

@@ -828,6 +828,7 @@ public void testColdStartupWithOnlyLastActiveTabUrl() {
                 mTabCreater, mHomeSurfaceTracker, mTabModelSelector, JUnitTestGURLs.URL_1, null);
         verify(mCurrentTabModel).addObserver(mTabModelObserverCaptor.capture());
 
+        // Verifies if the added Tab matches the tracking URL, call showHomeSurfaceUi().
         mTabModelObserverCaptor.getValue().willAddTab(mTab1, TabLaunchType.FROM_RESTORE);
         verify(mNewTabPage).showHomeSurfaceUi(eq(mTab1));
         verify(mHomeSurfaceTracker).updateHomeSurfaceAndTrackingTabs(eq(mNtpTab), eq(mTab1));