Don't force layout for mouse event hit tests

Source/core/page/EventHandler.cpp

Index: Source/core/page/EventHandler.cpp
diff --git a/Source/core/page/EventHandler.cpp b/Source/core/page/EventHandler.cpp
index 9a339bd89785e8814b5d0b6361fd02a41df373d4..d39f3d80e60915b55d080e916992ec8cb7d210af 100644
--- a/Source/core/page/EventHandler.cpp
+++ b/Source/core/page/EventHandler.cpp
@@ -939,7 +939,13 @@ HitTestResult EventHandler::hitTestResultAtPoint(const LayoutPoint& point, HitTe
 
     HitTestResult result(point, padding.height(), padding.width(), padding.height(), padding.width());
 
-    if (!m_frame->contentRenderer())
+    // RenderView::hitTest causes a layout, and we don't want to hit that until the first
+    // layout because until then, there is nothing shown on the screen - the user can't
+    // have intentionally clicked on something belonging to this page. Furthermore,
+    // mousemove events before the first layout should not lead to a premature layout()
+    // happening, which could show a flash of white.
+    // See also the similar code in Document::prepareMouseEvent.
+    if (!m_frame->contentRenderer() || !m_frame->view() || !m_frame->view()->didFirstLayout())
         return result;
 
     // hitTestResultAtPoint is specifically used to hitTest into all frames, thus it always allows child frame content.