Add missing 'using' declarations to fuchsia.web.Frame definition.

In future the fidlc tool will require explicit 'using' declarations for
all dependencies.

Bug: 879388
Change-Id: Ic82e6c7338d31e045ab20f24044fb97fbc151bbf
Reviewed-on: https://chromium-review.googlesource.com/1198012
Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587880}

webrunner/fidl/frame.fidl

@@ -4,6 +4,9 @@
 
 library chromium.web;
 
+using fuchsia.sys;
+using fuchsia.ui;
+
 interface Frame {
   // Creates and registers a view with the view manager and returns its
   // view owner which may subsequently be passed to |View.AddChild()|