Fix overflow/underflow in gfx geometry once and for all

ui/gfx/geometry/vector2d_unittest.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 <stddef.h>
 
 #include <cmath>
 #include <limits>
 
 #include "base/macros.h"
@@ skipping 231 matching lines @@
   a.SetToMin(Vector2dF(8.5f, 10.5f));
   EXPECT_EQ(Vector2dF(8.5f, 10.5f).ToString(), a.ToString());
   a.SetToMin(Vector2dF(11.5f, 9.5f));
   EXPECT_EQ(Vector2dF(8.5f, 9.5f).ToString(), a.ToString());
   a.SetToMin(Vector2dF(7.5f, 11.5f));
   EXPECT_EQ(Vector2dF(7.5f, 9.5f).ToString(), a.ToString());
   a.SetToMin(Vector2dF(3.5f, 5.5f));
   EXPECT_EQ(Vector2dF(3.5f, 5.5f).ToString(), a.ToString());
 }
 
+TEST(Vector2dTest, IntegerOverflow) {
+  int int_max = std::numeric_limits<int>::max();
+  int int_min = std::numeric_limits<int>::min();
+
+  Vector2d max_vector(int_max, int_max);
+  Vector2d min_vector(int_min, int_min);
+  Vector2d test;
+
+  test = Vector2d();
+  test += Vector2d(int_max, int_max);
+  EXPECT_EQ(test, max_vector);
+
+  test = Vector2d();
+  test += Vector2d(int_min, int_min);
+  EXPECT_EQ(test, min_vector);
+
+  test = Vector2d(10, 20);
+  test += Vector2d(int_max, int_max);
+  EXPECT_EQ(test, max_vector);
+
+  test = Vector2d(-10, -20);
+  test += Vector2d(int_min, int_min);
+  EXPECT_EQ(test, min_vector);
+
+  test = Vector2d();
+  test -= Vector2d(int_max, int_max);
+  EXPECT_EQ(test, Vector2d(-int_max, -int_max));
+
+  test = Vector2d();
+  test -= Vector2d(int_min, int_min);
+  EXPECT_EQ(test, max_vector);
+
+  test = Vector2d(10, 20);
+  test -= Vector2d(int_min, int_min);
+  EXPECT_EQ(test, max_vector);
+
+  test = Vector2d(-10, -20);
+  test -= Vector2d(int_max, int_max);
+  EXPECT_EQ(test, min_vector);
+}
+
 }  // namespace gfx