AW: re-enable flaky Safe Browsing test

No change to logic, this re-enables a test.

testSafeBrowsingWhitelistHardcodedWebUiPages was previously disabled
because it was flaking, although this may have been related to a
WebUI-related bug which paulmiller@ recently fixed (see
http://crrev/c/1432953).

This re-enables the test, since it seems reliable now.

R=paulmiller@chromium.org

Bug: 855732
Test: run_webview_instrumentation_test_apk --num_retries=0 \
Test: --break-on-failure --repeat=1000 \
Test: -f=SafeBrowsingTest.testSafeBrowsingWhitelistHardcodedWebUiPages
Change-Id: Idb890f5efdfc8777a679d476351aa421ec507a2b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1504042
Auto-Submit: Nate Fischer <ntfschr@chromium.org>
Reviewed-by: Paul Miller <paulmiller@chromium.org>
Commit-Queue: Paul Miller <paulmiller@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637813}

android_webview/javatests/src/org/chromium/android_webview/test/SafeBrowsingTest.java

@@ -549,7 +549,6 @@ public class SafeBrowsingTest {
         assertTargetPageHasLoaded(MALWARE_PAGE_BACKGROUND_COLOR);
     }
 
-    @DisabledTest(message = "crbug.com/855732")
     @Test
     @SmallTest
     @Feature({"AndroidWebView"})