Update from https://crrev.com/320931

ui/gfx/transform_unittest.cc

 // Copyright (c) 2011 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.
 
 // MSVC++ requires this to be set before any other includes to get M_PI.
 #define _USE_MATH_DEFINES
 
 #include "ui/gfx/transform.h"
 
 #include <cmath>
@@ skipping 2402 matching lines @@
   Transform A;
   InitializeTestMatrix(&A);
 
   A.FlattenTo2d();
   EXPECT_ROW1_EQ(10.0f, 14.0f, 0.0f, 22.0f, A);
   EXPECT_ROW2_EQ(11.0f, 15.0f, 0.0f, 23.0f, A);
   EXPECT_ROW3_EQ(0.0f,  0.0f,  1.0f, 0.0f,  A);
   EXPECT_ROW4_EQ(13.0f, 17.0f, 0.0f, 25.0f, A);
 }
 
+TEST(XFormTest, IsFlat) {
+  Transform transform;
+  InitializeTestMatrix(&transform);
+
+  // A transform with all entries non-zero isn't flat.
+  EXPECT_FALSE(transform.IsFlat());
+
+  transform.matrix().set(0, 2, 0.f);
+  transform.matrix().set(1, 2, 0.f);
+  transform.matrix().set(2, 2, 1.f);
+  transform.matrix().set(3, 2, 0.f);
+
+  EXPECT_FALSE(transform.IsFlat());
+
+  transform.matrix().set(2, 0, 0.f);
+  transform.matrix().set(2, 1, 0.f);
+  transform.matrix().set(2, 3, 0.f);
+
+  // Since the third column and row are both (0, 0, 1, 0), the transform is
+  // flat.
+  EXPECT_TRUE(transform.IsFlat());
+}
+
 // Another implementation of Preserves2dAxisAlignment that isn't as fast,
 // good for testing the faster implementation.
 static bool EmpiricallyPreserves2dAxisAlignment(const Transform& transform) {
   Point3F p1(5.0f, 5.0f, 0.0f);
   Point3F p2(10.0f, 5.0f, 0.0f);
   Point3F p3(10.0f, 20.0f, 0.0f);
   Point3F p4(5.0f, 20.0f, 0.0f);
 
   QuadF test_quad(PointF(p1.x(), p1.y()),
                  PointF(p2.x(), p2.y()),
@@ skipping 252 matching lines @@
   EXPECT_EQ(expected.ToString(), box.ToString());
 
   Transform singular;
   singular.Scale3d(0.f, 0.f, 0.f);
   EXPECT_FALSE(singular.TransformBoxReverse(&box));
 }
 
 }  // namespace
 
 }  // namespace gfx