ozone/wayland: Add UpdateBufferScale unittest

This adds a test for the previous CL: https://crrev.com/2564643

BUG=1113272

Change-Id: Ia43f3d0d788cb79ce4ec91baee5c0207660dfd52
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2566960Reviewed-by: Maksim Sisov (GMT+2) <msisov@igalia.com>
Commit-Queue: Zakhar Voit <zvoit@igalia.com>
Cr-Commit-Position: refs/heads/master@{#834664}

ui/ozone/platform/wayland/host/wayland_window_unittest.cc

@@ -34,6 +34,7 @@
 #include "ui/ozone/platform/wayland/test/mock_pointer.h"
 #include "ui/ozone/platform/wayland/test/mock_surface.h"
 #include "ui/ozone/platform/wayland/test/test_keyboard.h"
+#include "ui/ozone/platform/wayland/test/test_output.h"
 #include "ui/ozone/platform/wayland/test/test_region.h"
 #include "ui/ozone/platform/wayland/test/test_touch.h"
 #include "ui/ozone/platform/wayland/test/test_wayland_server_thread.h"
@@ -1397,6 +1398,45 @@ TEST_P(WaylandWindowTest, DispatchWindowResize) {
   }
 }
 
+TEST_P(WaylandWindowTest, ToplevelWindowUpdateBufferScale) {
+  VerifyAndClearExpectations();
+
+  // Buffer scale must be 1 when no output has been entered by the window.
+  EXPECT_EQ(1, window_->buffer_scale());
+
+  // Creating an output with scale 1.
+  wl::TestOutput* output1 = server_.CreateAndInitializeOutput();
+  output1->SetRect(gfx::Rect(0, 0, 1920, 1080));
+  output1->SetScale(1);
+  Sync();
+
+  // Creating an output with scale 2.
+  wl::TestOutput* output2 = server_.CreateAndInitializeOutput();
+  output2->SetRect(gfx::Rect(0, 0, 1920, 1080));
+  output2->SetScale(2);
+  Sync();
+
+  // Send the window to |output1|.
+  wl::MockSurface* surface = server_.GetObject<wl::MockSurface>(
+      window_->root_surface()->GetSurfaceId());
+  ASSERT_TRUE(surface);
+  wl_surface_send_enter(surface->resource(), output1->resource());
+  Sync();
+
+  // The window's scale and bounds must remain unchanged.
+  EXPECT_EQ(1, window_->buffer_scale());
+  EXPECT_EQ(gfx::Rect(0, 0, 800, 600), window_->GetBounds());
+
+  // Simulating drag process from |output1| to |output2|.
+  wl_surface_send_enter(surface->resource(), output2->resource());
+  wl_surface_send_leave(surface->resource(), output1->resource());
+  Sync();
+
+  // The window must change its scale and bounds to keep DIP bounds the same.
+  EXPECT_EQ(2, window_->buffer_scale());
+  EXPECT_EQ(gfx::Rect(0, 0, 1600, 1200), window_->GetBounds());
+}
+
 // Tests WaylandWindow repositions menu windows to be relative to parent window
 // in a right way.
 TEST_P(WaylandWindowTest, AdjustPopupBounds) {