Revert "Bug 1824053 - [1/4] Remove Win32 implementation of nsIWidget::SetBackgroundColor() r=win-reviewers,handyman"

This reverts commit e63e620.

Author: K4sum1

widget/nsIWidget.h

@@ -749,7 +749,7 @@ class nsIWidget : public nsISupports {
    * @param aShouldLock bool
    *
    */
-  virtual void LockAspectRatio(bool aShouldLock) {};
+  virtual void LockAspectRatio(bool aShouldLock){};
 
   /**
    * Move or resize this widget. Any size constraints set for the window by
@@ -928,11 +928,10 @@ class nsIWidget : public nsISupports {
   }
 
   /**
-   * Set the native background color for this widget.
-   *
-   * Deprecated. Currently only implemented for iOS. (See bug 1901896.)
+   * Set the background color for this widget
    *
    * @param aColor the new background color
+   *
    */
 
   virtual void SetBackgroundColor(const nscolor& aColor) {}
@@ -1986,7 +1985,7 @@ class nsIWidget : public nsISupports {
 
   virtual void UpdateZoomConstraints(
       const uint32_t& aPresShellId, const ScrollableLayerGuid::ViewID& aViewId,
-      const mozilla::Maybe<ZoomConstraints>& aConstraints) {};
+      const mozilla::Maybe<ZoomConstraints>& aConstraints){};
 
   /**
    * GetTextEventDispatcher() returns TextEventDispatcher belonging to the

widget/windows/nsWindow.cpp

@@ -703,6 +703,7 @@ static bool IsCloaked(HWND hwnd) {
 
 nsWindow::nsWindow(bool aIsChildWindow)
     : nsBaseWidget(BorderStyle::Default),
+      mBrush(::CreateSolidBrush(NSRGB_2_COLOREF(::GetSysColor(COLOR_BTNFACE)))),
       mFrameState(std::in_place, this),
       mIsChildWindow(aIsChildWindow),
       mLastPaintEndTime(TimeStamp::Now()),
@@ -1287,16 +1288,6 @@ static void RegisterWindowClass(const wchar_t* aClassName, UINT aExtraStyle,
       aIconID ? ::LoadIconW(::GetModuleHandleW(nullptr), aIconID) : nullptr;
   wc.lpszClassName = aClassName;
 
-  // Since we discard WM_ERASEBKGND events, the window-class background brush is
-  // mostly not used -- it shows up when resizing, but scarcely ever otherwise.
-  //
-  // In theory we could listen for theme changes and set this brush to an
-  // appropriate background color as needed; but given the hoops Win32 makes us
-  // jump through to change class data, it's probably not worth the trouble.
-  // (See bug 1901875.) Instead, we just make it dark grey, which is probably
-  // acceptable in either light or dark mode.
-  wc.hbrBackground = (HBRUSH)::GetStockObject(DKGRAY_BRUSH);
-
   // Failures are ignored as they are handled when ::CreateWindow fails
   ::RegisterClassW(&wc);
 }
@@ -2960,6 +2951,23 @@ HRGN nsWindow::ExcludeNonClientFromPaintRegion(HRGN aRegion) {
   return rgn;
 }
 
+/**************************************************************
+ *
+ * SECTION: nsIWidget::SetBackgroundColor
+ *
+ * Sets the window background paint color.
+ *
+ **************************************************************/
+
+void nsWindow::SetBackgroundColor(const nscolor& aColor) {
+  if (mBrush) ::DeleteObject(mBrush);
+
+  mBrush = ::CreateSolidBrush(NSRGB_2_COLOREF(aColor));
+  if (mWnd != nullptr) {
+    ::SetClassLongPtrW(mWnd, GCLP_HBRBACKGROUND, (LONG_PTR)mBrush);
+  }
+}
+
 /**************************************************************
  *
  * SECTION: nsIWidget::SetCursor
@@ -7505,6 +7513,12 @@ void nsWindow::OnDestroy() {
 
   IMEHandler::OnDestroyWindow(this);
 
+  // Free GDI window class objects
+  if (mBrush) {
+    VERIFY(::DeleteObject(mBrush));
+    mBrush = nullptr;
+  }
+
   // Destroy any custom cursor resources.
   if (mCursor.IsCustom()) {
     SetCursor(Cursor{eCursor_standard});

widget/windows/nsWindow.h

@@ -188,6 +188,7 @@ class nsWindow final : public nsBaseWidget {
   [[nodiscard]] nsresult GetRestoredBounds(LayoutDeviceIntRect& aRect) override;
   LayoutDeviceIntRect GetClientBounds() override;
   LayoutDeviceIntPoint GetClientOffset() override;
+  void SetBackgroundColor(const nscolor& aColor) override;
   void SetCursor(const Cursor&) override;
   bool PrepareForFullscreenTransition(nsISupports** aData) override;
   void PerformFullscreenTransition(FullscreenTransitionStage aStage,
@@ -739,6 +740,7 @@ class nsWindow final : public nsBaseWidget {
   HWND mWnd = nullptr;
   HWND mTransitionWnd = nullptr;
   mozilla::Maybe<WNDPROC> mPrevWndProc;
+  HBRUSH mBrush;
   IMEContext mDefaultIMC;
   HDEVNOTIFY mDeviceNotifyHandle = nullptr;
   bool mIsTopWidgetWindow = false;

xpfe/appshell/AppWindow.cpp

@@ -217,8 +217,8 @@ nsresult AppWindow::Initialize(nsIAppWindow* aParent, nsIAppWindow* aOpener,
   NS_ENSURE_SUCCESS(rv, rv);
 
   LayoutDeviceIntRect r = mWindow->GetClientBounds();
-  // Match the default background color of content. Previously important on
-  // Windows, but no longer has any effect there.
+  // Match the default background color of content. Important on windows
+  // since we no longer use content child widgets.
   mWindow->SetBackgroundColor(NS_RGB(255, 255, 255));
 
   // All Chrome BCs exist within the same BrowsingContextGroup, so we don't need