DevTools: introduce screencast experiment.

Source/devtools/protocol.json

 {
     "version": { "major": "1", "minor": "0" },
     "domains": [{
         "domain": "Inspector",
         "hidden": true,
         "types": [],
         "commands": [
             {
                 "name": "enable",
                 "description": "Enables inspector domain notifications."
@@ skipping 396 matching lines @@
                 "name": "setEmulatedMedia",
                 "parameters": [
                     { "name": "media", "type": "string", "description": "Media type to emulate. Empty string disables the override." }
                 ],
                 "description": "Emulates the given media for CSS media queries.",
                 "hidden": true
             },
             {
                 "name": "captureScreenshot",
                 "description": "Capture page screenshot.",
+                "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": "scale", "type": "number", "optional": true, "description": "Image scale from range [0..1]." }
+                ],
                 "returns": [
                     { "name": "data", "type": "string", "description": "Base64-encoded image data (PNG)." }
                 ]
             },
             {
+                "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": "scale", "type": "number", "optional": true, "description": "Image scale from range [0..1]." }
+                ],
+                "hidden": true
+            },
+            {
+                "name": "stopScreencast",
+                "description": "Stops sending each frame in the <code>screencastFrame</code>.",
+                "hidden": true
+            },
+            {
                 "name": "handleJavaScriptDialog",
                 "description": "Accepts or dismisses a JavaScript initiated dialog (alert, confirm, prompt, or onbeforeunload).",
                 "parameters": [
                     { "name": "accept", "type": "boolean", "description": "Whether to accept or dismiss the dialog." },
                     { "name": "promptText", "type": "string", "optional": true, "description": "The text to enter into the dialog prompt before accepting. Used only if this is a prompt dialog." }
                 ],
                 "hidden": true
             },
             {
                 "name": "setShowViewportSizeOnResize",
@@ skipping 88 matching lines @@
                 "description": "Fired when a JavaScript initiated dialog (alert, confirm, prompt, or onbeforeunload) has been closed.",
                 "hidden": true
             },
             {
                 "name": "scriptsEnabled",
                 "description": "Fired when the JavaScript is enabled/disabled on the page",
                 "parameters": [
                     { "name": "isEnabled", "type": "boolean", "description": "Whether script execution is enabled or disabled on the page." }
                 ],
                 "hidden": true
+            },
+            {
+                "name": "screencastFrame",
+                "description": "Compressed image data requested by the <code>startScreencast</code>.",
+                "parameters": [
+                    { "name": "data", "type": "string", "description": "Base64-encoded compressed image." }
+                ],
+                "hidden": true
             }
         ]
     },
     {
         "domain": "Runtime",
         "description": "Runtime domain exposes JavaScript runtime by means of remote evaluation and mirror objects. Evaluation results are returned as mirror object that expose object type, string representation and unique identifier that can be used for further object reference. Original objects are maintained in memory unless they are either explicitly released or are released along with the other objects in their object group.",
         "types": [
             {
                 "id": "RemoteObjectId",
                 "type": "string",
@@ skipping 3272 matching lines @@
                 "parameters": [
                     { "name": "value", "type": "array", "items": { "type": "object" } }
                 ]
             },
             {
                 "name": "tracingComplete"
             }
         ]
     }]
 }