WebView: add @NonNull annotation to API

No change to logic, only an annotation change.

startSafeBrowsing() should never receive a null Context. This adds
@NonNull to hint to developers not to pass null Contexts.

Test: N/A
Change-Id: I46d863047bf7563ea2a1adf592f3f381be95ca49
diff --git a/core/java/android/webkit/WebView.java b/core/java/android/webkit/WebView.java
index 65deb3b..538c789 100644
--- a/core/java/android/webkit/WebView.java
+++ b/core/java/android/webkit/WebView.java
@@ -1683,7 +1683,7 @@
      * @param callback will be called on the UI thread with {@code true} if initialization is
      * successful, {@code false} otherwise.
      */
-    public static void startSafeBrowsing(Context context,
+    public static void startSafeBrowsing(@NonNull Context context,
             @Nullable ValueCallback<Boolean> callback) {
         getFactory().getStatics().initSafeBrowsing(context, callback);
     }