Add Plumbing for WM_DPICHANGED

ui/views/win/hwnd_message_handler.cc

 // Copyright (c) 2012 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/views/win/hwnd_message_handler.h"
 
 #include <dwmapi.h>
 #include <oleacc.h>
 #include <shellapi.h>
 #include <tchar.h>
@@ skipping 10 matching lines @@
 #include "base/trace_event/trace_event.h"
 #include "base/win/scoped_gdi_object.h"
 #include "base/win/windows_version.h"
 #include "ui/base/touch/touch_enabled.h"
 #include "ui/base/view_prop.h"
 #include "ui/base/win/internal_constants.h"
 #include "ui/base/win/lock_state.h"
 #include "ui/base/win/mouse_wheel_util.h"
 #include "ui/base/win/shell.h"
 #include "ui/base/win/touch_input.h"
+#include "ui/display/win/dpi.h"
 #include "ui/events/event.h"
 #include "ui/events/event_utils.h"
 #include "ui/events/keycodes/keyboard_code_conversion_win.h"
 #include "ui/events/win/system_event_state_lookup.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/geometry/insets.h"
 #include "ui/gfx/icon_util.h"
 #include "ui/gfx/path.h"
 #include "ui/gfx/path_win.h"
 #include "ui/gfx/win/direct_manipulation.h"
@@ skipping 1347 matching lines @@
                                                     LPARAM l_param) {
   if (!delegate_->HasNonClientView()) {
     SetMsgHandled(FALSE);
     return 0;
   }
 
   FrameTypeChanged();
   return 0;
 }
 
+LRESULT HWNDMessageHandler::OnDpiChanged(UINT msg,
+                                         WPARAM w_param,
+                                         LPARAM l_param) {
+  // We assume square-style scaling factors.
+  DCHECK_EQ(LOWORD(w_param), HIWORD(w_param));

[sky, 2016/06/27 19:09:22]

Is this DCHECK really worthwhile? Presumably folks can still run on non-square
scales and would then hit this, right? What good would the DCHECK do?

[robliao, 2016/06/27 19:40:34]

The DCHECK is only worthwhile to the extent that this is one of the leading
edges of accepting scale factor information in Chrome. The other is when we
construct the displays, which would also trigger.

I can remove it if you want.

+  SetBoundsInternal(gfx::Rect(*reinterpret_cast<RECT*>(l_param)), false);
+  delegate_->HandleWindowScaleFactorChanged(
+      display::win::GetScalingFactorFromDPI(LOWORD(w_param)));
+  return 0;
+}
+
 void HWNDMessageHandler::OnEnterMenuLoop(BOOL from_track_popup_menu) {
   if (menu_depth_++ == 0)
     delegate_->HandleMenuLoop(true);
 }
 
 void HWNDMessageHandler::OnEnterSizeMove() {
   // Please refer to the comments in the OnSize function about the scrollbar
   // hack.
   // Hide the Windows scrollbar if the scroll styles are present to ensure
   // that a paint flicker does not occur while sizing.
@@ skipping 1328 matching lines @@
   MONITORINFO monitor_info = {sizeof(monitor_info)};
   GetMonitorInfo(MonitorFromWindow(hwnd(), MONITOR_DEFAULTTOPRIMARY),
                  &monitor_info);
   gfx::Rect shrunk_rect(monitor_info.rcMonitor);
   shrunk_rect.set_height(shrunk_rect.height() - 1);
   background_fullscreen_hack_ = true;
   SetBoundsInternal(shrunk_rect, false);
 }
 
 }  // namespace views