De-flake input-element-pseudo-open

test_driver.bless() calls were timing out while the picker is open, and
the color picker wasn't closing when calling input.blur(). Replacing
both of these with test_driver.click() on a button that always comes
before the pickers fixes both of these issues.

Change-Id: I01550d84c5e6111329cc660f6e797ce21f4e2b74
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6149610
Commit-Queue: Joey Arhar <[email protected]>
Reviewed-by: Steinar H Gunderson <[email protected]>
Reviewed-by: Di Zhang <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1402549}

css/css-pseudo/input-element-pseudo-open.optional.html

@@ -11,6 +11,8 @@
      varies across browsers and platforms. This test reflects picker support in
      desktop chromium. -->
 
+<button>reset</button>
+
 <div class=supported>
   <input type=date>
   <input type=datetime-local>
@@ -38,8 +40,7 @@
     assert_true(input.matches(':open'),
       'Should match :open after opening the picker.');
 
-    await test_driver.bless();
-    input.blur();
+    await test_driver.click(document.querySelector('button'));
     assert_false(input.matches(':open'),
       'Should not match :open after closing the picker.');
   }, `CSS :open for <input type=${inputType}>`);