DevTools: Split creating inspector stylesheet and adding a new rule into stylesheet in protocol.

Source/devtools/protocol.json

 {
     "version": { "major": "1", "minor": "1" },
     "domains": [{
         "domain": "Inspector",
         "hidden": true,
         "types": [],
         "commands": [
             {
                 "name": "enable",
                 "description": "Enables inspector domain notifications."
@@ skipping 2653 matching lines @@
                 "parameters": [
                     { "name": "ruleId", "$ref": "CSSRuleId" },
                     { "name": "selector", "type": "string" }
                 ],
                 "returns": [
                     { "name": "rule", "$ref": "CSSRule", "description": "The resulting rule after the selector modification." }
                 ],
                 "description": "Modifies the rule selector."
             },
             {
+                "name": "createStyleSheet",
+                "parameters": [
+                    { "name": "frameId", "$ref": "Page.FrameId", "description": "Identifier of the frame where \"via-inspector\" stylesheet should be created."}
+                ],
+                "returns": [
+                    { "name": "styleSheetId", "$ref": "StyleSheetId", "description": "Identifier of the created \"via-inspector\" stylesheet." }
+                ],
+                "description": "Creates a new special \"via-inspector\" stylesheet in the frame with given <code>frameId</code>."
+            },
+            {
                 "name": "addRule",
                 "parameters": [
-                    { "name": "contextNodeId", "$ref": "DOM.NodeId" },
+                    { "name": "styleSheetId", "$ref": "StyleSheetId" },
                     { "name": "selector", "type": "string" }
                 ],
                 "returns": [
                     { "name": "rule", "$ref": "CSSRule", "description": "The newly created rule." }
                 ],
-                "description": "Creates a new empty rule with the given <code>selector</code> in a special \"inspector\" stylesheet in the owner document of the context node."
+                "description": "Creates a new empty rule with the given <code>selector</code> in a stylesheet with given <code>styleSheetId</code>."
             },
             {
                 "name": "forcePseudoState",
                 "parameters": [
                     { "name": "nodeId", "$ref": "DOM.NodeId", "description": "The element id for which to force the pseudo state." },
                     { "name": "forcedPseudoClasses", "type": "array", "items": { "type": "string", "enum": ["active", "focus", "hover", "visited"] }, "description": "Element pseudo classes to force when computing the element's style." }
                 ],
                 "description": "Ensures that the given node will have specified pseudo-classes whenever its style is computed by the browser."
             }
         ],
@@ skipping 1351 matching lines @@
             {
                 "name": "dataAvailable",
                 "parameters": [
                     {"name": "value", "type": "array", "items": { "$ref": "PowerEvent" }, "description": "List of power events." }
                 ],
                 "handlers": ["browser", "frontend"]
             }
         ]
     }]
 }