DevTools: Load document (html) content from disk cache in page agent enabling.

Source/devtools/protocol.json

 {
     "version": { "major": "1", "minor": "1" },
     "domains": [{
         "domain": "Inspector",
         "hidden": true,
         "types": [],
         "commands": [
             {
                 "name": "enable",
                 "description": "Enables inspector domain notifications."
@@ skipping 2573 matching lines @@
                     { "name": "familyName", "type": "string", "description": "Font's family name reported by platform."},
                     { "name": "glyphCount", "type": "number", "description": "Amount of glyphs that were rendered with this font."}
                 ],
                 "description": "Information about amount of glyphs that were rendered with given font.",
                 "hidden": true
             }
         ],
         "commands": [
             {
                 "name": "enable",
-                "async": true,
                 "description": "Enables the CSS agent for the given page. Clients should not assume that the CSS agent has been enabled until the result of this command is received."
             },
             {
                 "name": "disable",
                 "description": "Disables the CSS agent for the given page."
             },
             {
                 "name": "getMatchedStylesForNode",
                 "parameters": [
                     { "name": "nodeId", "$ref": "DOM.NodeId" },
@@ skipping 1525 matching lines @@
             {
                 "name": "dataAvailable",
                 "parameters": [
                     {"name": "value", "type": "array", "items": { "$ref": "PowerEvent" }, "description": "List of power events." }
                 ],
                 "handlers": ["browser", "frontend"]
             }
         ]
     }]
 }