Keep effectiveZoom finite

LayoutTests/animations/zoomed-length-crash.html

Index: LayoutTests/animations/zoomed-length-crash.html
diff --git a/LayoutTests/animations/zoomed-length-crash.html b/LayoutTests/animations/zoomed-length-crash.html
new file mode 100644
index 0000000000000000000000000000000000000000..a10f7d366cd8a0005992ecdfc7e4315edd4dc8ee
--- /dev/null
+++ b/LayoutTests/animations/zoomed-length-crash.html
@@ -0,0 +1,24 @@
+<style>
+#target {
+  animation: anim 1s -0.25s step-start paused;
+}
+@keyframes anim {
+  50% {
+    left: 1000px;
+  }
+}
+* { zoom: 6318030279180000000; }
+</style>
+<div id=target></div>
+<p>PASS if no crash.</p>
+<script>
+if (window.testRunner) {
+  testRunner.dumpAsText();
+  testRunner.waitUntilDone();
+}
+target.addEventListener('animationstart', function() {
+  getComputedStyle(target).left;
+  if (window.testRunner)
+    testRunner.notifyDone();
+});
+</script>