Use alias_for with trivial property aliases

LayoutTests/fast/css/getComputedStyle/computed-style-expected.txt

 Attributes that are exposed in the CSS computed style object:
 
 background-attachment: scroll;
 background-clip: border-box;
 background-color: rgba(0, 0, 0, 0);
 background-image: none;
 background-origin: padding-box;
 background-position: 0% 0%;
 background-repeat: repeat;
 background-size: auto;
@@ skipping 97 matching lines @@
 zoom: 1;
 -webkit-animation-delay: 0s;
 -webkit-animation-direction: normal;
 -webkit-animation-duration: 0s;
 -webkit-animation-fill-mode: none;
 -webkit-animation-iteration-count: 1;
 -webkit-animation-name: none;
 -webkit-animation-play-state: running;
 -webkit-animation-timing-function: ease;
 -webkit-appearance: none;
--webkit-backface-visibility: visible;

[Timothy Loh, 2015/04/20 01:31:55]

alias_for properties are not enumerable

 -webkit-background-clip: border-box;
 -webkit-background-composite: source-over;
 -webkit-background-origin: padding-box;
 -webkit-background-size: auto;
 -webkit-border-horizontal-spacing: 0px;
 -webkit-border-image: none;
 -webkit-border-vertical-spacing: 0px;
 -webkit-box-align: stretch;
 -webkit-box-decoration-break: slice;
 -webkit-box-direction: normal;
 -webkit-box-flex: 0;
 -webkit-box-flex-group: 1;
 -webkit-box-lines: single;
 -webkit-box-ordinal-group: 1;
 -webkit-box-orient: horizontal;
 -webkit-box-pack: start;
 -webkit-box-reflect: none;
--webkit-box-shadow: none;
 -webkit-column-break-after: auto;
 -webkit-column-break-before: auto;
 -webkit-column-break-inside: auto;
 -webkit-column-count: auto;
 -webkit-column-gap: normal;
 -webkit-column-rule-color: rgb(0, 0, 0);
 -webkit-column-rule-style: none;
 -webkit-column-rule-width: 0px;
 -webkit-column-span: none;
 -webkit-column-width: auto;
@@ skipping 20 matching lines @@
 -webkit-mask-box-image-width: auto;
 -webkit-mask-clip: border-box;
 -webkit-mask-composite: source-over;
 -webkit-mask-image: none;
 -webkit-mask-origin: border-box;
 -webkit-mask-position: 0% 0%;
 -webkit-mask-repeat: repeat;
 -webkit-mask-size: auto;
 order: 0;
 -webkit-perspective: none;
--webkit-perspective-origin: 392px 288px;
 -webkit-print-color-adjust: economy;
 -webkit-rtl-ordering: logical;
 -webkit-text-combine: none;
 -webkit-text-decorations-in-effect: none;
 -webkit-text-emphasis-color: rgb(0, 0, 0);
 -webkit-text-emphasis-position: over;
 -webkit-text-emphasis-style: none;
 -webkit-text-fill-color: rgb(0, 0, 0);
 -webkit-text-orientation: vertical-right;
 -webkit-text-security: none;
 -webkit-text-stroke-color: rgb(0, 0, 0);
 -webkit-text-stroke-width: 0px;
 -webkit-transform: none;
--webkit-transform-origin: 392px 288px;
--webkit-transform-style: flat;
 -webkit-transition-delay: 0s;
 -webkit-transition-duration: 0s;
 -webkit-transition-property: all;
 -webkit-transition-timing-function: ease;
 -webkit-user-drag: auto;
 -webkit-user-modify: read-only;
 -webkit-user-select: text;
 -webkit-writing-mode: horizontal-tb;
 clip-path: none;
 clip-rule: nonzero;
@@ skipping 33 matching lines @@
 
 Other attributes that the computed style class supports:
 
 background-position-x: 0%;
 background-position-y: 0%;
 border-spacing: 0px 0px;
 overflow: visible;
 -webkit-mask-position-x: 0%;
 -webkit-mask-position-y: 0%;