Update to Chromium version 88.0.4324.0 (#827102)

- Mac: Xcode 12.2 and the MacOS 11.0 SDK are now required for building.
- MacOS 10.10 (Yosemite) is no longer supported (see https://crbug.com/1126056).
- Flash is no longer supported (see https://www.chromium.org/flash-roadmap).

libcef/renderer/browser_impl.h

@@ -77,9 +77,6 @@ class CefBrowserImpl : public CefBrowser, public content::RenderViewObserver {
   int browser_id() const { return browser_id_; }
   bool is_popup() const { return is_popup_; }
   bool is_windowless() const { return is_windowless_; }
-  content::RenderView* render_view() const {
-    return content::RenderViewObserver::render_view();
-  }
 
   // RenderViewObserver methods.
   void OnDestruct() override;