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/browser/frame_host_impl.h

@@ -87,6 +87,10 @@ class CefFrameHostImpl : public CefFrame {
   void SetFocused(bool focused);
   void RefreshAttributes();
 
+  // Notification that a move or resize of the renderer's containing window has
+  // started. Used on Windows and Linux with the Alloy runtime.
+  void NotifyMoveOrResizeStarted();
+
   // Navigate as specified by the |params| argument.
   void Navigate(const CefNavigateParams& params);