[inspector] introduced stepIntoAsync for chained callbacks

src/inspector/js_protocol.json

 {
     "version": { "major": "1", "minor": "2" },
     "domains": [
     {
         "domain": "Schema",
         "description": "Provides information about the protocol schema.",
         "types": [
             {
                 "id": "Domain",
                 "type": "object",
@@ skipping 540 matching lines @@
             },
             {
                 "name": "stepOver",
                 "description": "Steps over the statement."
             },
             {
                 "name": "stepInto",
                 "description": "Steps into the function call."
             },
             {
+                "name": "stepIntoAsync",
+                "description": "Steps into the scheduled callback."
+            },
+            {
                 "name": "stepOut",
                 "description": "Steps out of the function call."
             },
             {
                 "name": "pause",
                 "description": "Stops on the next JavaScript statement."
             },
             {
                 "name": "resume",
                 "description": "Resumes JavaScript execution."
@@ skipping 425 matching lines @@
             {
                 "name": "heapStatsUpdate",
                 "description": "If heap objects tracking has been started then backend may send update for one or more fragments",
                 "parameters": [
                     { "name": "statsUpdate", "type": "array", "items": { "type": "integer" }, "description": "An array of triplets. Each triplet describes a fragment. The first integer is the fragment index, the second integer is a total count of objects for the fragment, the third integer is a total size of the objects for the fragment."}
                 ]
             }
         ]
     }]
 }