Compute initial values for registered custom properties.

third_party/WebKit/LayoutTests/custom-properties/registered-property-initial.html

Index: third_party/WebKit/LayoutTests/custom-properties/registered-property-initial.html
diff --git a/third_party/WebKit/LayoutTests/custom-properties/registered-property-initial.html b/third_party/WebKit/LayoutTests/custom-properties/registered-property-initial.html
index 6a6ada6634f65887bfa60d83d0551443e6f7c2cb..91dcd4bb614c33479cc374441514f42de8a6ecda 100644
--- a/third_party/WebKit/LayoutTests/custom-properties/registered-property-initial.html
+++ b/third_party/WebKit/LayoutTests/custom-properties/registered-property-initial.html
@@ -9,11 +9,15 @@
 </style>
 <div id=target></div>
 <script>
+CSS.registerProperty({name: '--length', syntax: '<length>', initialValue: 'calc(10px + 15px)'});
+CSS.registerProperty({name: '--length-percentage', syntax: '<length-percentage>', initialValue: 'calc(1in + 10% + 4px)'});
 CSS.registerProperty({name: '--inherited-color', syntax: '<color>', initialValue: 'pink', inherits: true});
 CSS.registerProperty({name: '--non-inherited-color', syntax: '<color>', initialValue: 'purple'});
 
 test(function() {
     computedStyle = getComputedStyle(target);
+    assert_equals(computedStyle.getPropertyValue('--length'), '25px');
+    assert_equals(computedStyle.getPropertyValue('--length-percentage'), 'calc(100px + 10%)');
     assert_equals(computedStyle.getPropertyValue('--inherited-color'), 'pink');
     assert_equals(computedStyle.getPropertyValue('--non-inherited-color'), 'purple');