Remove support for the externalResourcesRequired attribute.

LayoutTests/http/tests/svg/svgload-vs-load.svg

Index: LayoutTests/http/tests/svg/svgload-vs-load.svg
diff --git a/LayoutTests/http/tests/svg/svgload-vs-load.svg b/LayoutTests/http/tests/svg/svgload-vs-load.svg
new file mode 100644
index 0000000000000000000000000000000000000000..64f4003ee6e8c9a2fc843a3a07a5a8011afb7765
--- /dev/null
+++ b/LayoutTests/http/tests/svg/svgload-vs-load.svg
@@ -0,0 +1,24 @@
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+  <script>
+	  if (window.testRunner) {
+		testRunner.waitUntilDone();
+		testRunner.dumpAsText();
+	  }
+
+	  window.onload = function() {
+        if (window.testRunner)
+          testRunner.notifyDone();
+	  };
+  </script>
+  <text y="170" x="20" id="console"/>
+  <script>
+      document.documentElement.addEventListener("load", loaded, false);
+      document.documentElement.addEventListener("SVGLoad", loaded, false);
+
+      function loaded(evt) {
+		document.getElementById("console").textContent += evt.type + "(" + evt.target.localName + ") ";
+      }
+  </script>
+  <image id="image" onload="loaded(evt)" onerror="loaded(evt)" x="20" y="20"
+   width="100" height="100" xlink:href="http://127.0.0.1:8000/svg/resources/delayCachedLoad.php" />
+</svg>