Emit console warning when element.animate() keyframe value fails to parse

third_party/WebKit/LayoutTests/animations/element-animate-keyframe-value-warning.html

Index: third_party/WebKit/LayoutTests/animations/element-animate-keyframe-value-warning.html
diff --git a/third_party/WebKit/LayoutTests/animations/element-animate-keyframe-value-warning.html b/third_party/WebKit/LayoutTests/animations/element-animate-keyframe-value-warning.html
new file mode 100644
index 0000000000000000000000000000000000000000..33756496ed8517146fc1e29fa68c723a9965d65d
--- /dev/null
+++ b/third_party/WebKit/LayoutTests/animations/element-animate-keyframe-value-warning.html
@@ -0,0 +1,15 @@
+<div id="target"></div>
+This test passes if there are three warnings about invalid keyframe values.
+<script>
+if (window.testRunner) {
+  testRunner.dumpAsText();
+}
+target.animate({offsetPath: ''});
+target.animate({offsetPath: 'path("m0 0")'});
+target.animate({offsetPath: 'path("invalid")'});
+target.animate({'--valid': ''});
+target.animate({'--x': 'valid'});
+target.animate({'--x': 'invalid )'});
+target.animate({'--x': 'invalid !important'});
+target.animate([{background: 'green', backgroundColor: 'green'}]);
+</script>