Reduce strictness of length animation DCHECK

third_party/WebKit/LayoutTests/animations/length-zero-percent-crash.html

Index: third_party/WebKit/LayoutTests/animations/length-zero-percent-crash.html
diff --git a/third_party/WebKit/LayoutTests/animations/length-zero-percent-crash.html b/third_party/WebKit/LayoutTests/animations/length-zero-percent-crash.html
new file mode 100644
index 0000000000000000000000000000000000000000..4e74f0d495390fa7f592e6c757a377e9c23315a3
--- /dev/null
+++ b/third_party/WebKit/LayoutTests/animations/length-zero-percent-crash.html
@@ -0,0 +1,9 @@
+<script src="../resources/testharness.js"></script>
+<script src="../resources/testharnessreport.js"></script>
+<div id="target"></div>
+<script>
+test(() => {
+  target.animate({margin: ['1px', '0%']}, {iterationStart: 0.5, fill: 'forwards'});
+  assert_equals(getComputedStyle(target).margin, '0.5px');
+}, "Don't crash when animating length properties to 0%");
+</script>