[iOS] Dismiss Activity View Popover In Context Menu Sharing EG Tests

Tapping anywhere else on the app (e.g. the keyWindow) will make the
popover disappear.

Bug: 1149618
Change-Id: If7f712cd3498b0a055a364d047105464d58492d0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2542366
Commit-Queue: Sebastien Lalancette <seblalancette@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827975}

ios/chrome/test/earl_grey/chrome_earl_grey.mm

@@ -1093,6 +1093,10 @@ GREY_STUB_CLASS_IN_APP_MAIN_QUEUE(ChromeEarlGreyAppInterface)
   // Page title is added asynchronously, so wait for its appearance.
   [self waitForMatcher:grey_allOf(ActivityViewHeader(pageTitle),
                                   grey_sufficientlyVisible(), nil)];
+
+  // Dismiss the Activity View by tapping outside its bounds.
+  [[EarlGrey selectElementWithMatcher:grey_keyWindow()]
+      performAction:grey_tap()];
 }
 
 #pragma mark - Unified consent utilities