Fix RGBA alpha parsing and serialization to adhere to W3 standard.

third_party/WebKit/LayoutTests/compositing/overflow/clear-scroll-parent-expected.txt

 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true
     },
     {
       "name": "LayoutBlockFlow DIV class='container'",
       "position": [8, 8],
       "bounds": [308, 208],
       "shouldFlattenTransform": false,
       "drawsContent": true,
-      "backgroundColor": "#00FF007F"
+      "backgroundColor": "#00FF0080"
     },
     {
       "name": "Scrolling Layer",
       "position": [4, 4],
       "bounds": [285, 200],
       "shouldFlattenTransform": false
     },
     {
       "name": "Scrolling Contents Layer",
       "bounds": [285, 530],
@@ skipping 27 matching lines @@
       "position": [12, 12],
       "bounds": [80, 80],
       "shouldFlattenTransform": false,
       "hasScrollParent": true
     },
     {
       "name": "LayoutBlockFlow (relative positioned) DIV class='box red'",
       "position": [10, 10],
       "bounds": [100, 100],
       "drawsContent": true,
-      "backgroundColor": "#FF00007F"
+      "backgroundColor": "#FF000080"
     },
     {
       "name": "Squashing Containment Layer",
       "shouldFlattenTransform": false,
       "hasScrollParent": true
     },
     {
       "name": "LayoutBlockFlow (relative positioned) DIV class='box'",
       "position": [22, 102],
       "bounds": [100, 100],
       "drawsContent": true,
-      "backgroundColor": "#0000FF7F"
+      "backgroundColor": "#0000FF80"
     },
     {
       "name": "Squashing Layer (first squashed layer: LayoutBlockFlow (relative positioned) DIV class='box')",
       "position": [22, 212],
       "bounds": [100, 320],
       "drawsContent": true
     }
   ]
 }