DevTools: Support asynchronous call stacks on backend.

Source/devtools/protocol.json

 {
     "version": { "major": "1", "minor": "1" },
     "domains": [{
         "domain": "Inspector",
         "hidden": true,
         "types": [],
         "commands": [
             {
                 "name": "enable",
                 "description": "Enables inspector domain notifications."
@@ skipping 3321 matching lines @@
                 "hidden": true,
                 "description": "Returns call stack including variables changed since VM was paused. VM must be paused."
             },
             {
                 "name": "skipStackFrames",
                 "parameters": [
                     { "name": "script", "optional": true, "type": "string", "description": "Regular expression defining the scripts to ignore while stepping." }
                 ],
                 "hidden": true,
                 "description": "Makes backend skip steps in the sources with names matching given pattern. VM will try leave blacklisted scripts by performing 'step in' several times, finally resorting to 'step out' if unsuccessful."
+            },
+            {
+                "name": "setAsyncCallStackDepth",
+                "parameters": [
+                    { "name": "maxDepth", "type": "integer", "description": "Maximum depth of async call stacks. Setting to <code>0</code> will effectively disable collecting async call stacks (default)." }
+                ],
+                "hidden": true,
+                "description": "Enables or disables async call stacks tracking."
             }
         ],
         "events": [
             {
                 "name": "globalObjectCleared",
                 "description": "Called when global has been cleared and debugger client should reset its state. Happens upon navigation or reload."
             },
             {
                 "name": "scriptParsed",
                 "parameters": [
@@ skipping 783 matching lines @@
                 ],
                 "handlers": ["browser", "frontend"]
             },
             {
                 "name": "tracingComplete",
                 "handlers": ["browser", "frontend"]
             }
         ]
     }]
 }