Disable VrBrowserJavaScriptModalDialogTest#testPromptModalDialog

The test has been consistently failing for the past few runs.
More details in the bug.

TBR=bsheedy@chromium.org

Bug: 902319
Change-Id: I9dbd161610a7bb3d9010e7b7a0e6fed802c74cc9
Reviewed-on: https://chromium-review.googlesource.com/c/1318920Reviewed-by: Rayan Kanso <rayankans@chromium.org>
Commit-Queue: Rayan Kanso <rayankans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605705}

chrome/android/javatests/src/org/chromium/chrome/browser/vr/jsdialog/VrBrowserJavaScriptModalDialogTest.java

@@ -17,6 +17,7 @@ import org.junit.runner.RunWith;
 
 import org.chromium.base.ThreadUtils;
 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.Restriction;
 import org.chromium.chrome.browser.ChromeSwitches;
@@ -79,6 +80,7 @@ public class VrBrowserJavaScriptModalDialogTest {
     @Test
     @MediumTest
     @Feature({"Browser", "RenderTest"})
+    @DisabledTest
     public void testPromptModalDialog() throws ExecutionException, IOException {
         testModalDialogImpl(
                 "js_modal_view_vr_prompt", "prompt('Is the tree closed?', 'Hopefully not')");