Use page popup pixel readback for calendar-picker-appearance.html

Source/core/page/PagePopupDriver.h

Index: Source/core/page/PagePopupDriver.h
diff --git a/Source/core/page/PagePopupDriver.h b/Source/core/page/PagePopupDriver.h
index 5e3c6f38696f5c146486757466a4af914a814a72..32c86f2452656179ee3243356dce2d221868d9fb 100644
--- a/Source/core/page/PagePopupDriver.h
+++ b/Source/core/page/PagePopupDriver.h
@@ -29,6 +29,7 @@
 namespace blink {
 
 class IntRect;
+class LocalDOMWindow;
 class PagePopup;
 class PagePopupClient;
 
@@ -36,6 +37,7 @@ class PagePopupDriver {
 public:
     virtual PagePopup* openPagePopup(PagePopupClient*, const IntRect& originBoundsInRootView) = 0;
     virtual void closePagePopup(PagePopup*) = 0;
+    virtual LocalDOMWindow* pagePopupWindow() = 0;
     virtual ~PagePopupDriver() { }
 };