DevTools: introduce screencast experiment.

Source/devtools/protocol.json

Index: Source/devtools/protocol.json
diff --git a/Source/devtools/protocol.json b/Source/devtools/protocol.json
index 5cb1ddff5b8ae7ca9a12579536db0c13b012d7a4..43f407929d91ff9f422003bff864bd2902ddbd3a 100644
--- a/Source/devtools/protocol.json
+++ b/Source/devtools/protocol.json
@@ -414,11 +414,31 @@
             {
                 "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": [
@@ -527,6 +547,14 @@
                     { "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
             }
         ]
     },