Bug 1647871 - Remove nsIWidget::GetCompositionSize(). r=kats

No longer called. This was done as an optimization for OOP iframes, but
it affects the scrollport so it's clearly not sound (the visible rect
shouldn't affect the layout scroll port).

If very tall OOP iframes are a problem somehow, it's something that we
need to deal with in another place. It was, in fact, removed for
top-level remote iframes because of bug 1554861 and other regressions.

Depends on D80731

Differential Revision: https://phabricator.services.mozilla.com/D80732

widget/PuppetWidget.cpp

@@ -1156,15 +1156,6 @@ LayoutDeviceIntRect PuppetWidget::GetScreenBounds() {
   return LayoutDeviceIntRect(WidgetToScreenOffset(), mBounds.Size());
 }
 
-LayoutDeviceIntSize PuppetWidget::GetCompositionSize() {
-  Maybe<LayoutDeviceIntRect> visibleRect =
-      mBrowserChild ? mBrowserChild->GetVisibleRect() : Nothing();
-  if (!visibleRect) {
-    return nsBaseWidget::GetCompositionSize();
-  }
-  return visibleRect->Size();
-}
-
 uint32_t PuppetWidget::GetMaxTouchPoints() const {
   return mBrowserChild ? mBrowserChild->MaxTouchPoints() : 0;
 }

widget/PuppetWidget.h

@@ -248,8 +248,6 @@ class PuppetWidget : public nsBaseWidget,
 
   virtual LayoutDeviceIntRect GetScreenBounds() override;
 
-  virtual LayoutDeviceIntSize GetCompositionSize() override;
-
   [[nodiscard]] virtual nsresult StartPluginIME(
       const mozilla::WidgetKeyboardEvent& aKeyboardEvent, int32_t aPanelX,
       int32_t aPanelY, nsString& aCommitted) override;

widget/nsIWidget.h

@@ -939,16 +939,6 @@ class nsIWidget : public nsISupports {
     return GetClientBounds().Size();
   }
 
-  /**
-   * Get the size of the bounds of this widget that will be visible when
-   * rendered.
-   *
-   * @return the width and height of the composition size of this widget.
-   */
-  virtual LayoutDeviceIntSize GetCompositionSize() {
-    return GetBounds().Size();
-  }
-
   /**
    * Set the background color for this widget
    *