[ios] Mark flaky tests in WebUITestCase

TBR=michaeldo@chromium.org

Bug: 1058028
Change-Id: I4bbb97da0dc5835a59da40d2b211142820d2a314
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2099480Reviewed-by: edchin <edchin@chromium.org>
Commit-Queue: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749494}

ios/chrome/browser/ui/webui/web_ui_egtest.mm

@@ -127,7 +127,8 @@ bool WaitForOmniboxURLString(std::string URL, bool exact_match = true) {
 
 // Tests that back navigation functions properly after navigation via anchor
 // click.
-- (void)testChromeURLBackNavigationFromAnchorClick {
+// TODO(crbug.com/1058028): This test is flaky.
+- (void)FLAKY_testChromeURLBackNavigationFromAnchorClick {
   [ChromeEarlGrey loadURL:GURL(kChromeUIChromeURLsURL)];
 
   // Tap on chrome://version link on the page.
@@ -218,7 +219,8 @@ bool WaitForOmniboxURLString(std::string URL, bool exact_match = true) {
 }
 
 // Tests that repeated back/forward navigation from web URL is allowed.
-- (void)testBackForwardFromWebURL {
+// TODO(crbug.com/1058028): This test is flaky.
+- (void)FLAKY_testBackForwardFromWebURL {
   GREYAssertTrue(self.testServer->Start(), @"Test server failed to start.");
 
   std::string chromeVersionWebText =