DevTools: Implement undo, redo operations for the DOMStorage views.

Source/devtools/protocol.json

 {
     "version": { "major": "1", "minor": "0" },
     "domains": [{
         "domain": "Inspector",
         "hidden": true,
         "types": [],
         "commands": [
             {
                 "name": "enable",
                 "description": "Enables inspector domain notifications."
@@ skipping 1420 matching lines @@
         "commands": [
             {
                 "name": "enable",
                 "description": "Enables storage tracking, storage events will now be delivered to the client."
             },
             {
                 "name": "disable",
                 "description": "Disables storage tracking, prevents storage events from being sent to the client."
             },
             {
+                "name": "getValue",
+                "parameters": [
+                    { "name": "storageId", "$ref": "StorageId" },
+                    { "name": "key", "type": "string" }
+                ],
+                "returns": [
+                    { "name": "value", "type": "string", "optional": true }
+                ]
+            },
+            {
                 "name": "getDOMStorageItems",
                 "parameters": [
                     { "name": "storageId", "$ref": "StorageId" }
                 ],
                 "returns": [
                     { "name": "entries", "type": "array", "items": { "$ref": "Item" } }
                 ]
             },
             {
                 "name": "setDOMStorageItem",
@@ skipping 2398 matching lines @@
                 "parameters": [
                     { "name": "value", "type": "array", "items": { "type": "object" } }
                 ]
             },
             {
                 "name": "tracingComplete"
             }
         ]
     }]
 }