[DevTools] Switch from DIP to CSS pixels in device mode.

Source/devtools/protocol.json

 {
     "version": { "major": "1", "minor": "1" },
     "domains": [{
         "domain": "Inspector",
         "hidden": true,
         "types": [],
         "commands": [
             {
                 "name": "enable",
                 "description": "Enables inspector domain notifications."
@@ skipping 172 matching lines @@
                 "id": "UsageItem",
                 "type": "object",
                 "description": "Usage information for a client and storage type",
                 "properties": [
                     { "name": "id", "type": "string", "enum": ["filesystem", "database", "appcache", "indexeddatabase"], "description": "Item id." },
                     { "name": "value", "type": "number", "description": "Item usage value." }
                 ],
                 "hidden": true
             },
             {
+                "id": "Viewport",
+                "type": "object",
+                "description": "Visible page viewport",
+                "properties": [
+                    { "name": "scrollX", "type": "number", "description": "X scroll offset in CSS pixels." },
+                    { "name": "scrollY", "type": "number", "description": "Y scroll offset in CSS pixels." },
+                    { "name": "contentsWidth", "type": "number", "description": "Contents width in CSS pixels." },
+                    { "name": "contentsHeight", "type": "number", "description": "Contents height in CSS pixels." },
+                    { "name": "pageScaleFactor", "type": "number", "description": "Page scale factor." }
+                ],
+                "hidden": true
+            },
+            {
                 "id": "ScreencastFrameMetadata",
                 "type": "object",
                 "description": "Screencast frame metadata",
                 "properties": [
                     { "name": "deviceScaleFactor", "type": "number", "hidden": true, "description": "Device scale factor." },
                     { "name": "viewport", "$ref": "DOM.Rect", "hidden": true, "description": "Viewport in CSS pixels." },
                     { "name": "offsetTop", "type": "number", "hidden": true, "optional": true, "description": "Top offset in DIP." },
                     { "name": "offsetBottom", "type": "number", "hidden": true, "optional": true, "description": "Bottom offset in DIP." },
                     { "name": "pageScaleFactor", "type": "number", "hidden": true, "description": "Page scale factor." },
                     { "name": "pageScaleFactorMin", "type": "number", "hidden": true, "description": "Page scale factor min." },
@@ skipping 438 matching lines @@
                 "handlers": ["browser"]
             },
             {
                 "name": "screencastVisibilityChanged",
                 "description": "Fired when the page with currently enabled screencast was shown or hidden </code>.",
                 "parameters": [
                     { "name": "visible", "type": "boolean", "description": "True if the page is visible." }
                 ],
                 "hidden": true,
                 "handlers": ["browser"]
+            },
+            {
+                "name": "viewportChanged",
+                "description": "Fired when a visible page viewport has changed.",
+                "parameters": [
+                    { "name": "viewport", "$ref": "Viewport", "description": "Viewport description." }
+                ],
+                "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 3546 matching lines @@
             {
                 "name": "dataAvailable",
                 "parameters": [
                     {"name": "value", "type": "array", "items": { "$ref": "PowerEvent" }, "description": "List of power events." }
                 ],
                 "handlers": ["browser", "frontend"]
             }
         ]
     }]
 }