Mark SafeBrowsingTest#testSafeBrowsingDontProceedNavigatesBackForSubResource as flaky.

TBR=ntfschr@chromium.org
BUG=822753

Change-Id: I0ff8b5d2b1a9d5abe930e80d8a21e886ab32c457
Reviewed-on: https://chromium-review.googlesource.com/966866Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543762}

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

@@ -46,6 +46,7 @@ import org.chromium.base.test.util.CallbackHelper;
 import org.chromium.base.test.util.CommandLineFlags;
 import org.chromium.base.test.util.DisabledTest;
 import org.chromium.base.test.util.Feature;
+import org.chromium.base.test.util.FlakyTest;
 import org.chromium.base.test.util.InMemorySharedPreferences;
 import org.chromium.base.test.util.RetryOnFailure;
 import org.chromium.components.safe_browsing.SafeBrowsingApiBridge;
@@ -656,6 +657,7 @@ public class SafeBrowsingTest {
     @Test
     @SmallTest
     @Feature({"AndroidWebView"})
+    @FlakyTest(message = "crbug/822753")
     public void testSafeBrowsingDontProceedNavigatesBackForSubResource() throws Throwable {
         loadGreenPage();
         final String originalTitle = mActivityTestRule.getTitleOnUiThread(mAwContents);