fix: fallback to FullSizeContentView for frameless window on mac (#13600)

When using `views::Widget` to create window, Chromium will automatically
use a `BridgedContentView` as content view, which however does not
support draggable regions inside it.

By fallback to `FullSizeContentView` we can work around this problem,
with the price of losing the ability to use `views::View` APIs. Since
we don't expect users to use the new `View` APIs in `BrowserWindow`
anyway, it should not be a problem.

This change does not affect users of `TopLevelWindow`, and for users of
`BrowserWindow` there is nothing to lose.

In the long term we should look into how to make draggable regions work
with `BridgedContentView`. The related Chromium code is still being
changed rapidly, we can wait until Chromium migrated its
`NativeAppWindowCocoa` class to use `views::Widget`.

atom/browser/api/atom_api_browser_window.cc

@@ -85,6 +85,11 @@ BrowserWindow::BrowserWindow(v8::Isolate* isolate,
 
   InitWith(isolate, wrapper);
 
+#if defined(OS_MACOSX)
+  if (!window()->has_frame())
+    OverrideNSWindowContentView();
+#endif
+
   // Init window after everything has been setup.
   window()->InitFromOptions(options);
 }

atom/browser/api/atom_api_browser_window.h

@@ -80,6 +80,10 @@ class BrowserWindow : public TopLevelWindow,
   v8::Local<v8::Value> GetWebContents(v8::Isolate* isolate);
 
  private:
+#if defined(OS_MACOSX)
+  void OverrideNSWindowContentView();
+#endif
+
   // Helpers.
 
   // Called when the window needs to update its draggable region.

atom/browser/api/atom_api_browser_window_mac.mm

@@ -7,6 +7,7 @@
 #import <Cocoa/Cocoa.h>
 
 #include "atom/browser/native_browser_view.h"
+#include "atom/browser/native_window_mac.h"
 #include "atom/common/draggable_region.h"
 #include "base/mac/scoped_nsobject.h"
 
@@ -53,6 +54,17 @@ std::vector<gfx::Rect> CalculateNonDraggableRegions(
 
 }  // namespace
 
+void BrowserWindow::OverrideNSWindowContentView() {
+  // Make NativeWindow use a NSView as content view.
+  static_cast<NativeWindowMac*>(window())->OverrideNSWindowContentView();
+  // Add webview to contentView.
+  NSView* webView = web_contents()->GetNativeView();
+  NSView* contentView = [window()->GetNativeWindow() contentView];
+  [webView setFrame:[contentView bounds]];
+  [contentView addSubview:webView];
+  [contentView viewDidMoveToWindow];
+}
+
 void BrowserWindow::UpdateDraggableRegions(
     content::RenderFrameHost* rfh,
     const std::vector<DraggableRegion>& regions) {