[iOS] Ensure correct tab grid mode for search scrim test.

testScrimVisibleInSearchModeWhenSearchBarIsEmpty was disabled due to
flake. Images of the test state for these failures showed the tab grid
on the recent tabs panel; successful test runs are on the normal tabs
panel.

This CL adds a step to move to the regular tabs panel at the start of
the test.

Fixed: 1359271
Change-Id: I69f0ec2ffc56c86efad84ef68be3c5f17714a2fc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3925616
Auto-Submit: Mark Cogan <marq@chromium.org>
Reviewed-by: David Jean <djean@chromium.org>
Commit-Queue: David Jean <djean@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1052886}

ios/chrome/browser/ui/tab_switcher/tab_grid/tab_grid_egtest.mm

@@ -1434,11 +1434,14 @@ - (void)testTabGridResetAfterExitingSearch {
 
 // Tests that the scrim view is always shown when the search bar is empty in the
 // search mode.
-// TODO(crbug.com/1359271): Disabled due to flakiness. Re-enabled when fixed.
-- (void)DISABLED_testScrimVisibleInSearchModeWhenSearchBarIsEmpty {
+- (void)testScrimVisibleInSearchModeWhenSearchBarIsEmpty {
   [ChromeEarlGrey openNewTab];
   [ChromeEarlGreyUI openTabGrid];
 
+  // Make sure the tab grid is on the regular tabs panel.
+  [[EarlGrey selectElementWithMatcher:TabGridNormalModePageControl()]
+      performAction:grey_tap()];
+
   // Enter search mode.
   [[EarlGrey selectElementWithMatcher:TabGridSearchTabsButton()]
       performAction:grey_tap()];