Compute minimum repaint and show them in overlay

Source/core/testing/Internals.cpp

Index: Source/core/testing/Internals.cpp
diff --git a/Source/core/testing/Internals.cpp b/Source/core/testing/Internals.cpp
index 58ae5411fb34bc30aa723a12ad376b036497acfe..eebdb1dd264eafe0045beed154d1cd265a94c6be 100644
--- a/Source/core/testing/Internals.cpp
+++ b/Source/core/testing/Internals.cpp
@@ -2038,6 +2038,17 @@ void Internals::updateLayoutIgnorePendingStylesheetsAndRunPostLayoutTasks(Node*
     document->updateLayoutIgnorePendingStylesheets(Document::RunPostLayoutTasksSynchronously);
 }
 
+void Internals::forceFullRepaint(Document* document, ExceptionState& exceptionState)
+{
+    if (!document || !document->view()) {
+        exceptionState.throwDOMException(InvalidAccessError, document ? "The document's view cannot be retrieved." : "The document provided is invalid.");
+        return;
+    }
+
+    if (RenderView *renderView = document->renderView())
+        renderView->repaintViewAndCompositedLayers();
+}
+
 PassRefPtrWillBeRawPtr<ClientRectList> Internals::draggableRegions(Document* document, ExceptionState& exceptionState)
 {
     return annotatedRegions(document, true, exceptionState);