chrome窗口

chrome 窗口的层次：

父窗口类名：Chrome_WidgetWin_1

有两个子窗口：

Chrome_RenderWidgetHostHWND
Intermediate D3D Window

// 用于匹配 Chrome 窗口的窗口类的前缀。

onst wchar_t kChromeWindowClassPrefix[] = L"Chrome_WidgetWin_";

const wchar_t kLegacyRenderWidgetHostHwnd[] = L"Chrome_RenderWidgetHostHWND";

Chrome_RenderWidgetHostHWND 窗口的作用：

content/browser/renderer_host/legacy_render_widget_host_win.h

// Reasons for the existence of this class outlined below:-
// 1. Some screen readers expect every tab / every unique web content container
//    to be in its own HWND with class name Chrome_RenderWidgetHostHWND.
//    With Aura there is one main HWND which comprises the whole browser window
//    or the whole desktop. So, we need a fake HWND with the window class as
//    Chrome_RenderWidgetHostHWND as the root of the accessibility tree for
//    each tab.
// 2. There are legacy drivers for trackpads/trackpoints which have special
//    code for sending mouse wheel and scroll events to the
//    Chrome_RenderWidgetHostHWND window.
// 3. Windowless NPAPI plugins like Flash and Silverlight which expect the
//    container window to have the same bounds as the web page. In Aura, the
//    default container window is the whole window which includes the web page
//    WebContents, etc. This causes the plugin mouse event calculations to
//    fail.
//    We should look to get rid of this code when all of the above are fixed.// This class implements a child HWND with the same size as the content area,
// that delegates its accessibility implementation to the root of the
// BrowserAccessibilityManager tree. This HWND is hooked up as the parent of
// the root object in the BrowserAccessibilityManager tree, so when any
// accessibility client calls ::WindowFromAccessibleObject, they get this
// HWND instead of the DesktopWindowTreeHostWin.

此类存在的原因概述如下：-
1. 一些屏幕阅读器期望每个选项卡/每个唯一的 Web 内容容器位于其自己的 HWND 中，类名为 Chrome_RenderWidgetHostHWND。对于 Aura，有一个主要的 HWND，它包含整个浏览器窗口
或整个桌面。所以，我们需要一个假的 HWND，其窗口类为Chrome_RenderWidgetHostHWND 作为可访问性树的根每个选项卡。
2. 触控板/轨迹点有一些遗留驱动程序，它们具有特殊的功能发送鼠标滚轮和滚动事件的代码
Chrome_RenderWidgetHostHWND 窗口。
3. Flash 和 Silverlight 等无窗口 NPAPI 插件需要容器窗口与网页具有相同的边界。在奥拉中，
默认容器窗口是包含网页的整个窗口WebContents 等。这会导致插件鼠标事件计算失败。
当上述所有问题都解决后，我们应该考虑删除这段代码。

这个类实现了一个与内容区域大小相同的子HWND，将其可访问性实现委托给根
BrowserAccessibilityManager 树。该 HWND 作为父级连接 BrowserAccessibilityManager 树中的根对象，因此当任何可访问性客户端调用::WindowFromAccessibleObject，他们得到这个HWND 而不是 DesktopWindowTreeHostWin。

ui/gl/child_window_win.h

DirectComposition 渲染到的窗口需要由进程拥有当前正在进行渲染。该类创建并拥有一个窗口
浏览器将其重新设置为其窗口的子窗口。

// This runs on the window owner thread.
void InitializeWindowClass() {if (g_window_class)return;WNDCLASSEX intermediate_class;base::win::InitializeWindowClass(L"Intermediate D3D Window",&base::win::WrappedWindowProc<::DefWindowProc>, CS_OWNDC, 0, 0, nullptr,reinterpret_cast<HBRUSH>(GetStockObject(BLACK_BRUSH)), nullptr, nullptr,nullptr, &intermediate_class);g_window_class = RegisterClassEx(&intermediate_class);if (!g_window_class) {LOG(ERROR) << "RegisterClass failed.";return;}
}