DevTools: Initial implementation of slow CPU emulation.

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.",
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                 "handlers": ["browser", "renderer"]
             },
             {
                 "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."
             },
             {
+                "name": "setCPUThrottlingRate",
+                "parameters": [
+                    { "name": "rate", "type": "number", "description": "Throttling rate as a slowdown factor (1 is no throttle, 2 is 2x slowdown, etc)." }
+                ],
+                "description": "Enables CPU throttling to emulate slow CPUs."
+            },
+            {
                 "name": "canEmulate",
                 "description": "Tells whether emulation is supported.",
                 "returns": [
                     { "name": "result", "type": "boolean", "description": "True if emulation is supported." }
                 ],
                 "handlers": ["browser"]
             }
         ],
         "events": [
             {
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                 ],
                 "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
             }
         ]
     }]
 }