ios: Work around flake in testXClientData.

Bug: 1120723
Change-Id: Id1a510e5bd318df12207169a06c58dd2090ff297
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2369437
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Rohit Rao <rohitrao@chromium.org>
Auto-Submit: Justin Cohen <justincohen@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#800687}

ios/chrome/browser/ui/omnibox/omnibox_egtest.mm

@@ -163,6 +163,12 @@ id<GREYMatcher> SearchCopiedTextButton() {
     EARL_GREY_TEST_SKIPPED(@"testXClientData doesn't pass on iPad device.");
   }
 #endif
+
+  // TODO(crbug.com/1120723) This test is flakily because of a DCHECK in
+  // ios/web.  Clearing browser history first works around the problem, but
+  // shouldn't be necessary otherwise.  Remove once the bug is fixed.
+  [ChromeEarlGrey clearBrowsingHistory];
+
   // Rewrite the google URL to localhost URL.
   [OmniboxAppInterface rewriteGoogleURLToLocalhost];