Use enclosing rect to find WindowTreeHost size.

ui/aura/window_tree_host_unittest.cc

+// Copyright 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 "ui/aura/test/aura_test_base.h"
+#include "ui/aura/test/test_screen.h"
+#include "ui/aura/window.h"
+#include "ui/compositor/layer.h"
+
+namespace aura {
+
+using WindowTreeHostTest = test::AuraTestBase;
+
+TEST_F(WindowTreeHostTest, DPIWindowSize) {
+  gfx::Rect starting_bounds(0, 0, 800, 600);
+  EXPECT_EQ(starting_bounds.size(), host()->compositor()->size());
+  EXPECT_EQ(starting_bounds, host()->GetBounds());
+  EXPECT_EQ(starting_bounds, root_window()->bounds());
+
+  test_screen()->SetDeviceScaleFactor(1.5f);
+  EXPECT_EQ(starting_bounds, host()->GetBounds());
+  // Size should be rounded up after scaling.
+  EXPECT_EQ(gfx::Rect(0, 0, 534, 400), root_window()->bounds());
+
+  gfx::Transform transform;
+  transform.Translate(0, 1.1f);
+  host()->SetRootTransform(transform);
+  EXPECT_EQ(gfx::Rect(0, 1, 534, 401), root_window()->bounds());
+
+  gfx::Insets padding(1, 2, 3, 4);
+  // Padding is in physical pixels.
+  host()->SetOutputSurfacePadding(padding);
+  gfx::Rect padded_rect = starting_bounds;
+  padded_rect.Inset(-padding);
+  EXPECT_EQ(padded_rect.size(), host()->compositor()->size());
+  EXPECT_EQ(starting_bounds, host()->GetBounds());
+  EXPECT_EQ(gfx::Rect(1, 1, 534, 401), root_window()->bounds());
+  EXPECT_EQ(gfx::Vector2dF(0, 0),
+            host()->compositor()->root_layer()->subpixel_position_offset());
+}
+
+}  // namespace aura