Disable failing KeyPrefixTest cases.

TBR=hnakashima@chromium.org

Bug: 1028821
Change-Id: I8d5b9d9a92f9ae4bd5d587fa2b4bcb4ad3ddc960
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1938044Reviewed-by: Ender <ender@google.com>
Commit-Queue: Ender <ender@google.com>
Cr-Commit-Position: refs/heads/master@{#719464}

chrome/browser/preferences/android/java/src/org/chromium/chrome/browser/preferences/KeyPrefixTest.java

@@ -11,6 +11,7 @@ import android.support.test.filters.SmallTest;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 
+import org.chromium.base.test.util.DisabledTest;
 import org.chromium.chrome.test.ChromeJUnit4ClassRunner;
 
 /**
@@ -29,18 +30,21 @@ public class KeyPrefixTest {
     }
 
     @Test(expected = AssertionError.class)
+    @DisabledTest(message = "https://crbug.com/1028821")
     @SmallTest
     public void testError_missingPeriod() {
         new KeyPrefix("Chrome.Feature.KP");
     }
 
     @Test(expected = AssertionError.class)
+    @DisabledTest(message = "https://crbug.com/1028821")
     @SmallTest
     public void testError_missingStar() {
         new KeyPrefix("Chrome.Feature.KP.");
     }
 
     @Test(expected = AssertionError.class)
+    @DisabledTest(message = "https://crbug.com/1028821")
     @SmallTest
     public void testError_extraStar() {
         new KeyPrefix("Chrome.Feature.KP.**");