Don't center screen magnification on empty focus rectangle

ash/magnifier/magnification_controller.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/magnifier/magnification_controller.h"
 
 #include <utility>
 
 #include "ash/accelerators/accelerator_controller.h"
 #include "ash/accessibility_delegate.h"
@@ skipping 417 matching lines @@
   return gfx::ToEnclosingRect(GetWindowRectDIP(scale_));
 }
 
 void MagnificationControllerImpl::HandleFocusedNodeChanged(
     bool is_editable_node,
     const gfx::Rect& node_bounds_in_screen) {
   // The editable node is handled by OnCaretBoundsChanged.
   if (is_editable_node)
     return;
 
+  // Nothing to recenter on.
+  if (node_bounds_in_screen.IsEmpty())
+    return;
+
   gfx::Rect node_bounds_in_root =
       ScreenUtil::ConvertRectFromScreen(root_window_, node_bounds_in_screen);
   if (GetViewportRect().Contains(node_bounds_in_root))
     return;
 
   MoveMagnifierWindowFollowRect(node_bounds_in_root);
 }
 
 void MagnificationControllerImpl::SwitchTargetRootWindow(
     aura::Window* new_root_window,
@@ skipping 401 matching lines @@
 
 ////////////////////////////////////////////////////////////////////////////////
 // MagnificationController:
 
 // static
 MagnificationController* MagnificationController::CreateInstance() {
   return new MagnificationControllerImpl();
 }
 
 }  // namespace ash