LibWebView: Add OOPWV "content scales to viewport" hint

By setting this hint, you indicate to OOPWV that the content inside will
scale itself to the viewport size. In such situations, it's fine for
OOPWV to reuse a scaled version of an outdated backing store while the
view is being resized.

Userland/Libraries/LibWebView/OutOfProcessWebView.cpp

@@ -106,7 +106,10 @@ void OutOfProcessWebView::paint_event(GUI::PaintEvent& event)
     if (auto* bitmap = m_client_state.has_usable_bitmap ? m_client_state.front_bitmap.bitmap.ptr() : m_backup_bitmap.ptr()) {
         painter.add_clip_rect(frame_inner_rect());
         painter.translate(frame_thickness(), frame_thickness());
-        painter.blit({ 0, 0 }, *bitmap, bitmap->rect());
+        if (m_content_scales_to_viewport)
+            painter.draw_scaled_bitmap(rect(), *bitmap, bitmap->rect());
+        else
+            painter.blit({ 0, 0 }, *bitmap, bitmap->rect());
         return;
     }
 
@@ -841,4 +844,9 @@ void OutOfProcessWebView::notify_server_did_get_accessibility_tree(DeprecatedStr
         on_get_accessibility_tree(accessibility_tree);
 }
 
+void OutOfProcessWebView::set_content_scales_to_viewport(bool b)
+{
+    m_content_scales_to_viewport = b;
+}
+
 }

Userland/Libraries/LibWebView/OutOfProcessWebView.h

@@ -80,6 +80,10 @@ public:
     Gfx::ShareableBitmap take_screenshot() const;
     Gfx::ShareableBitmap take_document_screenshot();
 
+    // This is a hint that tells OOPWV that the content will scale to the viewport size.
+    // In practice, this means that OOPWV may render scaled stale versions of the content while resizing.
+    void set_content_scales_to_viewport(bool);
+
     Function<void(Gfx::IntPoint screen_position)> on_context_menu_request;
     Function<void(const AK::URL&, DeprecatedString const& target, unsigned modifiers)> on_link_click;
     Function<void(const AK::URL&, Gfx::IntPoint screen_position)> on_link_context_menu_request;
@@ -225,6 +229,8 @@ private:
 
     bool m_is_awaiting_response_for_input_event { false };
     Queue<InputEvent> m_pending_input_events;
+
+    bool m_content_scales_to_viewport { false };
 };
 
 }