DevTools: Throttle Screencast on slow connections (Blink side)

Source/devtools/protocol.json

 {
     "version": { "major": "1", "minor": "1" },
     "domains": [{
         "domain": "Inspector",
         "hidden": true,
         "types": [],
         "commands": [
             {
                 "name": "enable",
                 "description": "Enables inspector domain notifications."
@@ skipping 525 matching lines @@
                 "hidden": true,
                 "handlers": ["browser", "renderer"]
             },
             {
                 "name": "stopScreencast",
                 "description": "Stops sending each frame in the <code>screencastFrame</code>.",
                 "hidden": true,
                 "handlers": ["browser", "renderer"]
             },
             {
+                "name": "screencastFrameAck",
+                "description": "Acknowledges that a screencast frame has been received by the frontend.",
+                "parameters": [
+                    { "name": "frameNumber", "type": "integer", "description": "Frame number." }
+                ],
+                "hidden": true,
+                "handlers": ["browser"]
+            },
+            {
                 "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,
                 "handlers": ["browser"]
             },
             {
@@ skipping 128 matching lines @@
                 "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." },
-                    { "name": "metadata", "$ref": "ScreencastFrameMetadata", "description": "Screencast frame metadata"}
+                    { "name": "metadata", "$ref": "ScreencastFrameMetadata", "description": "Screencast frame metadata."},
+                    { "name": "frameNumber", "type": "integer", "optional": true, "description": "Frame number."}
                 ],
                 "hidden": true,
                 "handlers": ["browser"]
             },
             {
                 "name": "screencastVisibilityChanged",
                 "description": "Fired when the page with currently enabled screencast was shown or hidden </code>.",
                 "parameters": [
                     { "name": "visible", "type": "boolean", "description": "True if the page is visible." }
                 ],
@@ skipping 3839 matching lines @@
                     { "name": "isRunning", "type": "boolean", "description": "If the animation player is still running." }
                 ],
                 "description": "Gets the state of an AnimationPlayer.",
                 "hidden": true
             }
         ],
         "events": [
         ]
     }]
 }