Add ImageLoader support for sizes based Client-Hints RW values

Source/core/html/HTMLImageElement.h

Index: Source/core/html/HTMLImageElement.h
diff --git a/Source/core/html/HTMLImageElement.h b/Source/core/html/HTMLImageElement.h
index e02d583247e51678491a420e09055ef0baa88d4d..1528c1b015c9d47eed869ad2b8c4cda4683358bf 100644
--- a/Source/core/html/HTMLImageElement.h
+++ b/Source/core/html/HTMLImageElement.h
@@ -107,6 +107,8 @@ public:
     void setUseFallbackContent();
     void setIsFallbackImage() { m_isFallbackImage = true; }
 
+    float sourceSize(Element&);
+
 protected:
     explicit HTMLImageElement(Document&, HTMLFormElement* = 0, bool createdByParser = false);