Null check

 Bug: 5021967
 Check if ACCESSIBILITY_SERVICE is null. Documentation claims this
 is acceptable, and it probably is happening due to low memory

Change-Id: Ie12059236baedd8b149831ad24da74f79453fae8
diff --git a/src/com/android/browser/BrowserActivity.java b/src/com/android/browser/BrowserActivity.java
index 1e1698b..b6d269d 100644
--- a/src/com/android/browser/BrowserActivity.java
+++ b/src/com/android/browser/BrowserActivity.java
@@ -79,8 +79,9 @@
             return;
         }
 
-        if (((AccessibilityManager) getSystemService(ACCESSIBILITY_SERVICE))
-                .isEnabled()) {
+        AccessibilityManager accessibilityManager = (AccessibilityManager)
+                getSystemService(ACCESSIBILITY_SERVICE);
+        if (accessibilityManager != null && accessibilityManager.isEnabled()) {
             setDefaultKeyMode(DEFAULT_KEYS_DISABLE);
         }