Devtools Animations: Add cubic bezier easing editor for animations

Source/devtools/protocol.json

 {
     "version": { "major": "1", "minor": "1" },
     "domains": [{
         "domain": "Inspector",
         "hidden": true,
         "types": [],
         "commands": [
             {
                 "name": "enable",
                 "description": "Enables inspector domain notifications.",
@@ skipping 4821 matching lines @@
                 "description": "Sets the current time of the document timeline."
             },
             {
                 "name": "setTiming",
                 "parameters": [
                     { "name": "playerId", "type": "string", "description": "AnimationPlayer id." },
                     { "name": "duration", "type": "number", "description": "Duration of the animation." },
                     { "name": "delay", "type": "number", "description": "Delay of the animation." }
                 ],
                 "description": "Sets the timing of an animation node."
+            },
+            {
+                "name": "setEasing",
+                "parameters": [
+                    { "name": "playerId", "type": "string", "description": "AnimationPlayer id." },
+                    { "name": "easing", "type": "string", "description": "Easing of the animation." }
+                ],
+                "description": "Sets the easing of an animation node."
             }
         ],
         "events": [
             {
                 "name": "animationPlayerCreated",
                 "parameters": [
                     { "name": "player", "$ref": "AnimationPlayer", "description": "AnimationPlayer that was created." },
                     { "name": "resetTimeline", "type": "boolean", "description": "Whether the timeline should be reset." }
                 ],
                 "description": "Event for each animation player that has been created."
@@ skipping 125 matching lines @@
                 ],
                 "returns": [
                     { "name": "accessibilityNode", "$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
             }
         ]
     }]
 }