Enable DisabletestModalNativeAppBannerCanBeTriggeredMultipleTimesCustomTab

This CL reverts half of https://crrev.com/c/1329161 by enabling
testModalNativeAppBannerCanBeTriggeredMultipleTimesCustomTab
that was disabled by the CL. The issue that was causing the failures
should've been fixed by https://crrev.com/c/1345069.
testAppInstalledModalNativeAppBannerCustomTab, the second test disabled
by https://crrev.com/c/1329161 is not enabled by this CL, as it fails
with TimeoutException (doesn't seem to be connected to the failure fixed
by https://crrev.com/c/1345069).

Bug: 903657
Change-Id: I4ef52c1bfe9d560fecbcfa4e389baffef758fe15
Reviewed-on: https://chromium-review.googlesource.com/c/1350187Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: Boris Sazonov <bsazonov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#613057}

chrome/android/javatests/src/org/chromium/chrome/browser/banners/AppBannerManagerTest.java

@@ -599,7 +599,6 @@ public class AppBannerManagerTest {
     @Test
     @SmallTest
     @Feature({"AppBanners"})
-    @DisabledTest(message = "crbug.com/903658")
     public void testModalNativeAppBannerCanBeTriggeredMultipleTimesCustomTab() throws Exception {
         mCustomTabActivityTestRule.startCustomTabActivityWithIntent(
                 CustomTabsTestUtils.createMinimalCustomTabIntent(