Fix the "call to 'abs' is ambiguous" error in line 42

ash/wm/workspace/two_step_edge_cycler.cc

 // Copyright 2014 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/wm/workspace/two_step_edge_cycler.h"
 
-#include <cmath>
+#include <cstdlib>
 
 namespace ash {
 namespace {
 
 // We cycle to the second mode if any of the following happens while the mouse
 // is on the edge of the workspace:
 // . The user stops moving the mouse for |kMaxDelay| and then moves the mouse
 //   again.
 // . The mouse moves |kMaxPixels| horizontal pixels.
 // . The mouse is moved |kMaxMoves| times.
@@ skipping 20 matching lines @@
   ++num_moves_;
   second_mode_ =
       (base::TimeTicks::Now() - time_last_move_).InMilliseconds() >
           kMaxDelay ||
       std::abs(location.x() - start_x_) >= kMaxPixels ||
       num_moves_ >= kMaxMoves;
   time_last_move_ = base::TimeTicks::Now();
 }
 
 }  // namespace ash