Avoid duplicate math when computing VR scene hierarchy.

chrome/browser/android/vr_shell/ui_scene_unittest.cc

 // Copyright (c) 2016 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 "chrome/browser/android/vr_shell/ui_scene.h"
 
 #define _USE_MATH_DEFINES  // For M_PI in MSVC.
 #include <cmath>
 #include <utility>
 #include <vector>
@@ skipping 108 matching lines @@
   element->size = {1, 1, 1};
   element->scale = {2, 2, 1};
   element->rotation = {0, 0, 1, M_PI / 2};
   element->translation = {3, 0, 0};
   scene.AddUiElement(std::move(element));
   const ContentRectangle* child = scene.GetUiElementById(1);
 
   const gvr::Vec3f origin({0, 0, 0});
   const gvr::Vec3f point({1, 0, 0});
 
-  // Check resulting transform with no screen tilt.
   scene.UpdateTransforms(0);
   auto new_origin = MatrixVectorMul(child->TransformMatrix(), origin);
   auto new_point = MatrixVectorMul(child->TransformMatrix(), point);
   EXPECT_VEC3F_NEAR(gvr::Vec3f({6, 10, 0}), new_origin);
   EXPECT_VEC3F_NEAR(gvr::Vec3f({0, 10, 0}), new_point);
 }
 
 TEST(UiScene, Opacity) {
   UiScene scene;
 
@@ skipping 294 matching lines @@
   EXPECT_FLOAT_EQ(animation->from[0], 300);
   EXPECT_FLOAT_EQ(animation->from[1], 301);
   EXPECT_FLOAT_EQ(animation->from[2], 302);
   EXPECT_FLOAT_EQ(animation->from[3], 303);
 
   EXPECT_EQ(animation->start, 22345000);
   EXPECT_EQ(animation->duration, 54321000);
 }
 
 }  // namespace vr_shell