Disable AccessibilityAriaGrabbed due to flakiness

BUG=453485
TBR=rouslan@chromium.org

Review URL: https://codereview.chromium.org/871193007

Cr-Commit-Position: refs/heads/master@{#313755}

content/browser/accessibility/dump_accessibility_tree_browsertest.cc

@@ -262,7 +262,8 @@ IN_PROC_BROWSER_TEST_F(DumpAccessibilityTreeTest, AccessibilityAriaForm) {
   RunAriaTest(FILE_PATH_LITERAL("aria-form.html"));
 }
 
-IN_PROC_BROWSER_TEST_F(DumpAccessibilityTreeTest, AccessibilityAriaGrabbed) {
+IN_PROC_BROWSER_TEST_F(DumpAccessibilityTreeTest,
+                       DISABLED_AccessibilityAriaGrabbed) {
   RunAriaTest(FILE_PATH_LITERAL("aria-grabbed.html"));
 }