[SVG] Skip layout viewport change calculation when not needed.

LayoutTests/svg/custom/viewport-resource-inval.svg

Index: LayoutTests/svg/custom/viewport-resource-inval.svg
diff --git a/LayoutTests/svg/custom/viewport-resource-inval.svg b/LayoutTests/svg/custom/viewport-resource-inval.svg
new file mode 100644
index 0000000000000000000000000000000000000000..1ba7386d882a16ab6dacb3377231f3e70f102033
--- /dev/null
+++ b/LayoutTests/svg/custom/viewport-resource-inval.svg
@@ -0,0 +1,41 @@
+<svg id="svg" width="200" height="200" version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+  <defs>
+    <mask id="mask">
+      <rect width="25%" height="25%" fill="white"/>
+    </mask>
+
+    <clipPath id="clip">
+      <rect x="27%" width="25%" height="25%"/>
+    </clipPath>
+
+    <pattern id="pattern" patternUnits="userSpaceOnUse" x="0" y="0" width="800" height="800">
+      <rect x="54%" width="25%" height="25%" fill="green"/>
+    </pattern>
+  </defs>
+
+  <rect width="25%" height="25%" fill="red"/>
+  <rect width="800" height="800" fill="green" mask="url(#mask)"/>
+
+  <rect x="27%" width="25%" height="25%" fill="red"/>
+  <rect width="800" height="800" fill="green" clip-path="url(#clip)"/>
+
+  <rect x="54%" width="25%" height="25%" fill="red"/>
+  <rect width="800" height="800" fill="url(#pattern)"/>
+
+  <script>
+    var delay=250;
+    if (window.testRunner) {
+      delay=0;
+      testRunner.waitUntilDone();
+    }
+
+    setTimeout(function() {
+      document.getElementById('svg').setAttribute('width', '400');
+      document.getElementById('svg').setAttribute('height', '400');
+
+      if (window.testRunner)
+        testRunner.notifyDone();
+    }, delay);
+  </script>
+</svg>
+