Bug 1503656 - Part 4. Add safe area to nsIWidget. r=emilio

Safe area value is stored in nsIWidget for each platform support

Differential Revision: https://phabricator.services.mozilla.com/D52508

--HG--
extra : moz-landing-system : lando

widget/nsIWidget.h

@@ -372,6 +372,7 @@ class nsIWidget : public nsISupports {
   typedef mozilla::LayoutDeviceIntRegion LayoutDeviceIntRegion;
   typedef mozilla::LayoutDeviceIntSize LayoutDeviceIntSize;
   typedef mozilla::ScreenIntPoint ScreenIntPoint;
+  typedef mozilla::ScreenIntMargin ScreenIntMargin;
   typedef mozilla::ScreenIntSize ScreenIntSize;
   typedef mozilla::ScreenPoint ScreenPoint;
   typedef mozilla::CSSToScreenScale CSSToScreenScale;
@@ -1742,6 +1743,14 @@ class nsIWidget : public nsISupports {
   }
 #endif
 
+  /*
+   * Get safe area insets except to cutout.
+   * See https://drafts.csswg.org/css-env-1/#safe-area-insets.
+   */
+  virtual mozilla::ScreenIntMargin GetSafeAreaInsets() const {
+    return mozilla::ScreenIntMargin();
+  }
+
  private:
   class LongTapInfo {
    public: