Update from https://crrev.com/320931

ui/gfx/transform_unittest.cc

Index: ui/gfx/transform_unittest.cc
diff --git a/ui/gfx/transform_unittest.cc b/ui/gfx/transform_unittest.cc
index ef801ac15e39cf7f5045568f2bf7c440b7744e55..aee6d8c6ebf7200acb85d9f8aff2297aadff8ef9 100644
--- a/ui/gfx/transform_unittest.cc
+++ b/ui/gfx/transform_unittest.cc
@@ -2420,6 +2420,29 @@ TEST(XFormTest, verifyFlattenTo2d) {
   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) {