Added Accessibility EG Tests for Download Manager UI.

Added the following tests:
 - testAccessibilityOnNotStartedDownloadToolbar
 - testAccessibilityOnCompletedDownloadToolbar

Bug: 854232
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I2c49197f02881548cdae817a9753798507ddfc3b
Reviewed-on: https://chromium-review.googlesource.com/1184323Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Commit-Queue: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585517}

ios/chrome/browser/ui/download/download_manager_egtest.mm

@@ -8,6 +8,7 @@
 #include "ios/chrome/browser/chrome_url_constants.h"
 #include "ios/chrome/grit/ios_strings.h"
 #import "ios/chrome/test/app/tab_test_util.h"
+#include "ios/chrome/test/earl_grey/accessibility_util.h"
 #import "ios/chrome/test/earl_grey/chrome_earl_grey.h"
 #import "ios/chrome/test/earl_grey/chrome_earl_grey_ui.h"
 #import "ios/chrome/test/earl_grey/chrome_matchers.h"
@@ -160,4 +161,30 @@ bool WaitForOpenInButton() {
   GREYAssert(WaitForOpenInButton(), @"Open in... button did not show up");
 }
 
+// Tests accessibility on Download Manager UI when download is not started.
+- (void)testAccessibilityOnNotStartedDownloadToolbar {
+  [ChromeEarlGrey loadURL:self.testServer->GetURL("/")];
+  [ChromeEarlGrey waitForWebViewContainingText:"Download"];
+  [ChromeEarlGrey tapWebViewElementWithID:@"download"];
+
+  [[EarlGrey selectElementWithMatcher:DownloadButton()]
+      assertWithMatcher:grey_notNil()];
+
+  chrome_test_util::VerifyAccessibilityForCurrentScreen();
+}
+
+// Tests accessibility on Download Manager UI when download is complete.
+- (void)testAccessibilityOnCompletedDownloadToolbar {
+  [ChromeEarlGrey loadURL:self.testServer->GetURL("/")];
+  [ChromeEarlGrey waitForWebViewContainingText:"Download"];
+  [ChromeEarlGrey tapWebViewElementWithID:@"download"];
+
+  [[EarlGrey selectElementWithMatcher:DownloadButton()]
+      performAction:grey_tap()];
+
+  GREYAssert(WaitForOpenInButton(), @"Open in... button did not show up");
+
+  chrome_test_util::VerifyAccessibilityForCurrentScreen();
+}
+
 @end