Delete SoftwareOutputDeviceWinDirectChild.

This software output device implementation created a child window to
draw into from the GPU process. This was to prevent some flashes in the
blank areas of the window on resize. While investigating
https://crbug.com/924975 it seems like drawing directly into the browser
HWND no longer causes any issues on Windows 7 or 10.

Drawing directly in the browser HWND also fixes the bug where we aren't
redrawing exposed regions on Windows 7 with DWM disabled and software
compositing. This was caused by the WM_PAINT update region being empty
for the browser window because it has the WS_CLIPCHILDREN style. The
child window wasn't handling the WM_PAINT message and with DWM disabled
Windows doesn't keep it's own copy of the pixels. As a result, nothing
was telling the display compositor to paint those pixels again.

Bug: 924975, 835906
Change-Id: I70eef78223ea6f18f4898ebb4d973811fa85c1d2
Reviewed-on: https://chromium-review.googlesource.com/c/1450399
Commit-Queue: kylechar <kylechar@chromium.org>
Reviewed-by: Sunny Sachanandani <sunnyps@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628433}

components/viz/service/display_embedder/software_output_device_win.cc

@@ -8,7 +8,6 @@
 #include "base/memory/shared_memory.h"
 #include "base/threading/thread_checker.h"
 #include "base/win/windows_version.h"
-#include "base/win/wrapped_window_proc.h"
 #include "components/viz/common/display/use_layered_window.h"
 #include "components/viz/common/resources/resource_sizes.h"
 #include "components/viz/service/display_embedder/output_device_backing.h"
@@ -17,7 +16,6 @@
 #include "skia/ext/platform_canvas.h"
 #include "skia/ext/skia_utils_win.h"
 #include "third_party/skia/include/core/SkCanvas.h"
-#include "ui/base/win/hidden_window.h"
 #include "ui/gfx/gdi_util.h"
 #include "ui/gfx/skia_util.h"
 #include "ui/gfx/win/hwnd_util.h"
@@ -336,96 +334,6 @@ void SoftwareOutputDeviceWinProxy::DrawAck() {
   std::move(swap_ack_callback_).Run();
 }
 
-// WindowProc callback function for SoftwareOutputDeviceWinDirectChild.
-LRESULT CALLBACK IntermediateWindowProc(HWND window,
-                                        UINT message,
-                                        WPARAM w_param,
-                                        LPARAM l_param) {
-  switch (message) {
-    case WM_ERASEBKGND:
-      // Prevent Windows from erasing all window content on resize.
-      return 1;
-    default:
-      return DefWindowProc(window, message, w_param, l_param);
-  }
-}
-
-// SoftwareOutputDevice implementation that creates a child HWND and draws
-// directly to it. This is intended to be used in the GPU process. The child
-// HWND is initially parented to a hidden window and needs be reparented to the
-// appropriate browser HWND. The backing buffer for paint is shared for all
-// instances of this class.
-class SoftwareOutputDeviceWinDirectChild
-    : public SoftwareOutputDeviceWinDirect {
- public:
-  static std::unique_ptr<SoftwareOutputDeviceWinDirectChild> Create(
-      OutputDeviceBacking* backing);
-  ~SoftwareOutputDeviceWinDirectChild() override;
-
-  // SoftwareOutputDeviceWinBase implementation.
-  void ResizeDelegated() override;
-
- private:
-  static wchar_t* GetWindowClass();
-
-  SoftwareOutputDeviceWinDirectChild(HWND child_hwnd,
-                                     OutputDeviceBacking* backing);
-
-  DISALLOW_COPY_AND_ASSIGN(SoftwareOutputDeviceWinDirectChild);
-};
-
-// static
-std::unique_ptr<SoftwareOutputDeviceWinDirectChild>
-SoftwareOutputDeviceWinDirectChild::Create(OutputDeviceBacking* backing) {
-  // Create a child window that is initially parented to a hidden window.
-  // |child_hwnd| needs to be reparented to a browser created HWND to be
-  // visible.
-  HWND child_hwnd =
-      CreateWindowEx(WS_EX_NOPARENTNOTIFY, GetWindowClass(), L"",
-                     WS_CHILDWINDOW | WS_DISABLED | WS_VISIBLE, 0, 0, 0, 0,
-                     ui::GetHiddenWindow(), nullptr, nullptr, nullptr);
-  DCHECK(child_hwnd);
-  return base::WrapUnique(
-      new SoftwareOutputDeviceWinDirectChild(child_hwnd, backing));
-}
-
-SoftwareOutputDeviceWinDirectChild::~SoftwareOutputDeviceWinDirectChild() {
-  DestroyWindow(hwnd());
-}
-
-void SoftwareOutputDeviceWinDirectChild::ResizeDelegated() {
-  SoftwareOutputDeviceWinDirect::ResizeDelegated();
-  // Resize the child HWND to match the content size.
-  SetWindowPos(hwnd(), nullptr, 0, 0, viewport_pixel_size_.width(),
-               viewport_pixel_size_.height(),
-               SWP_NOMOVE | SWP_NOACTIVATE | SWP_NOCOPYBITS |
-                   SWP_NOOWNERZORDER | SWP_NOZORDER);
-}
-
-// static
-wchar_t* SoftwareOutputDeviceWinDirectChild::GetWindowClass() {
-  static ATOM window_class = 0;
-
-  // Register window class on first call.
-  if (!window_class) {
-    WNDCLASSEX intermediate_class;
-    base::win::InitializeWindowClass(
-        L"Intermediate Software Window",
-        &base::win::WrappedWindowProc<IntermediateWindowProc>, CS_OWNDC, 0, 0,
-        nullptr, reinterpret_cast<HBRUSH>(GetStockObject(BLACK_BRUSH)), nullptr,
-        nullptr, nullptr, &intermediate_class);
-    window_class = RegisterClassEx(&intermediate_class);
-    DCHECK(window_class);
-  }
-
-  return reinterpret_cast<wchar_t*>(window_class);
-}
-
-SoftwareOutputDeviceWinDirectChild::SoftwareOutputDeviceWinDirectChild(
-    HWND child_hwnd,
-    OutputDeviceBacking* backing)
-    : SoftwareOutputDeviceWinDirect(child_hwnd, backing) {}
-
 }  // namespace
 
 std::unique_ptr<SoftwareOutputDevice> CreateSoftwareOutputDeviceWinBrowser(
@@ -442,6 +350,8 @@ std::unique_ptr<SoftwareOutputDevice> CreateSoftwareOutputDeviceWinGpu(
     OutputDeviceBacking* backing,
     mojom::DisplayClient* display_client,
     HWND* out_child_hwnd) {
+  // TODO(kylechar): Remove |out_child_hwnd| parameter it's no longer used.
+
   if (NeedsToUseLayerWindow(hwnd)) {
     DCHECK(display_client);
 
@@ -456,13 +366,7 @@ std::unique_ptr<SoftwareOutputDevice> CreateSoftwareOutputDeviceWinGpu(
     return std::make_unique<SoftwareOutputDeviceWinProxy>(
         hwnd, std::move(layered_window_updater));
   } else {
-    auto software_output_device =
-        SoftwareOutputDeviceWinDirectChild::Create(backing);
-
-    // The child HWND needs to be parented to the browser HWND to be visible.
-    *out_child_hwnd = software_output_device->hwnd();
-
-    return software_output_device;
+    return std::make_unique<SoftwareOutputDeviceWinDirect>(hwnd, backing);
   }
 }