DevTools: optimize screencast for slower devices.

third_party/WebKit/Source/devtools/protocol.json

 {
     "version": { "major": "1", "minor": "1" },
     "domains": [{
         "domain": "Inspector",
         "hidden": true,
         "types": [],
         "commands": [
             {
                 "name": "enable",
                 "description": "Enables inspector domain notifications.",
@@ skipping 395 matching lines @@
                 "hidden": true,
                 "handlers": ["browser"]
             },
             {
                 "name": "startScreencast",
                 "description": "Starts sending each frame using the <code>screencastFrame</code> event.",
                 "parameters": [
                     { "name": "format", "type": "string", "optional": true, "enum": ["jpeg", "png"], "description": "Image compression format." },
                     { "name": "quality", "type": "integer", "optional": true, "description": "Compression quality from range [0..100]." },
                     { "name": "maxWidth", "type": "integer", "optional": true, "description": "Maximum screenshot width." },
-                    { "name": "maxHeight", "type": "integer", "optional": true, "description": "Maximum screenshot height." }
+                    { "name": "maxHeight", "type": "integer", "optional": true, "description": "Maximum screenshot height." },
+                    { "name": "everyNthFrame", "type": "integer", "optional": true, "description": "Send every n-th frame." }
                 ],
                 "hidden": true,
                 "handlers": ["browser", "renderer"]
             },
             {
                 "name": "stopScreencast",
                 "description": "Stops sending each frame in the <code>screencastFrame</code>.",
                 "hidden": true,
                 "handlers": ["browser", "renderer"]
             },
@@ skipping 4873 matching lines @@
                 ],
                 "returns": [
                     { "name": "accessibilityNode", "$ref": "AXNode", "description": "The <code>Accessibility.AXNode</code> for this DOM node, if it exists.", "optional": true }
                 ],
                 "description": "Fetches the accessibility node for this DOM node, if it exists.",
                 "hidden": true
             }
         ]
     }]
 }