Use srcset's resource pixel density to determine intrinsic size

LayoutTests/fast/hidpi/image-srcset-dpr-zoom.html

Index: LayoutTests/fast/hidpi/image-srcset-dpr-zoom.html
diff --git a/LayoutTests/fast/hidpi/image-srcset-dpr-zoom.html b/LayoutTests/fast/hidpi/image-srcset-dpr-zoom.html
index f1586d8139e47a4d60d3c0852eb076fa66e95ec0..3f17244ddfa815442dd682c82f294d95b90c0ad9 100644
--- a/LayoutTests/fast/hidpi/image-srcset-dpr-zoom.html
+++ b/LayoutTests/fast/hidpi/image-srcset-dpr-zoom.html
@@ -9,10 +9,6 @@
 </script>
 <script src="../js/resources/js-test-pre.js"></script>
 <script>
-    if (window.testRunner) {
-        testRunner.dumpAsText();
-    }
-
     function updateSrc() {
         var img = document.getElementById("foo");
         img.srcset = "resources/blue-100-px-square.png 1x, resources/green-200-px-square.png 2x";