DevTools: expose layer compositing reasons and paint count via layer tree agent

Source/devtools/protocol.json

 {
     "version": { "major": "1", "minor": "0" },
     "domains": [{
         "domain": "Inspector",
         "hidden": true,
         "types": [],
         "commands": [
             {
                 "name": "enable",
                 "description": "Enables inspector domain notifications."
@@ skipping 3791 matching lines @@
                     { "name": "offsetX", "type": "number", "description": "Offset from parent layer, X coordinate." },
                     { "name": "offsetY", "type": "number", "description": "Offset from parent layer, X coordinate." },
                     { "name": "width", "type": "number", "description": "Layer width." },
                     { "name": "height", "type": "number", "description": "Layer height." },
                     { "name": "transform", "type": "array", "items": { "type": "number" }, "minItems": 16, "maxItems": 16, "optional": true, "description": "Transformation matrix for layer, default is identity matrix" },
                     { "name": "anchorX", "type": "number", "optional": true, "description": "Transform anchor point X, absent if no transform specified" },
                     { "name": "anchorY", "type": "number", "optional": true, "description": "Transform anchor point Y, absent if no transform specified" },
                     { "name": "anchorZ", "type": "number", "optional": true, "description": "Transform anchor point Z, absent if no transform specified" },
                     { "name": "paintCount", "type": "integer", "description": "Indicates how many time this layer has painted." }
                 ]
+            },
+            {
+                "id": "CompositingReasons",
+                "type": "object",
+                "description": "An object containing the reasons why the layer was composited as properties.",
+                "properties": [
+                    { "name": "transform3D", "type": "boolean", "optional": true, "description": "Composition due to association with an element with a CSS 3D transform." },

[pfeldman, 2013/08/22 16:49:54]

No! Please make this a dictionary!

+                    { "name": "video", "type": "boolean", "optional": true, "description": "Composition due to association with a <video> element." },
+                    { "name": "canvas", "type": "boolean", "optional": true, "description": "Composition due to the element being a <canvas> element." },
+                    { "name": "plugin", "type": "boolean", "optional": true, "description": "Composition due to association with a plugin." },
+                    { "name": "iFrame", "type": "boolean", "optional": true, "description": "Composition due to association with an <iframe> element." },
+                    { "name": "backfaceVisibilityHidden", "type": "boolean", "optional": true, "description": "Composition due to association with an element with a \"backface-visibility: hidden\" style." },
+                    { "name": "animation", "type": "boolean", "optional": true, "description": "Composition due to association with an animated element." },
+                    { "name": "filters", "type": "boolean", "optional": true, "description": "Composition due to association with an element with CSS filters applied." },
+                    { "name": "positionFixed", "type": "boolean", "optional": true, "description": "Composition due to association with an element with a \"position: fixed\" style." },
+                    { "name": "positionSticky", "type": "boolean", "optional": true, "description": "Composition due to association with an element with a \"position: sticky\" style." },
+                    { "name": "overflowScrollingTouch", "type": "boolean", "optional": true, "description": "Composition due to association with an element with a \"overflow-scrolling: touch\" style." },
+                    { "name": "blending", "type": "boolean", "optional": true, "description": "Composition due to association with an element that has blend mode other than \"normal\"." },
+                    { "name": "assumedOverlap", "type": "boolean", "optional": true, "description": "Composition due to association with an element that may overlap some of its composited children." },
+                    { "name": "overlap", "type": "boolean", "optional": true, "description": "Composition due to association with an element overlapping other composited elements." },
+                    { "name": "negativeZIndexChildren", "type": "boolean", "optional": true, "description": "Composition due to association with an element with descendants that have a negative z-index." },
+                    { "name": "transformWithCompositedDescendants", "type": "boolean", "optional": true, "description": "Composition due to association with an element with composited descendants." },
+                    { "name": "opacityWithCompositedDescendants", "type": "boolean", "optional": true, "description": "Composition due to association with an element with opacity applied and composited descendants." },
+                    { "name": "maskWithCompositedDescendants", "type": "boolean", "optional": true, "description": "Composition due to association with a masked element and composited descendants." },
+                    { "name": "reflectionWithCompositedDescendants", "type": "boolean", "optional": true, "description": "Composition due to association with an element with a reflection and composited descendants." },
+                    { "name": "filterWithCompositedDescendants", "type": "boolean", "optional": true, "description": "Composition due to association with an element with CSS filters applied and composited descendants." },
+                    { "name": "blendingWithCompositedDescendants", "type": "boolean", "optional": true, "description": "Composition due to association with an element with CSS blending applied and composited descendants." },
+                    { "name": "clipsCompositingDescendants", "type": "boolean", "optional": true, "description": "Composition due to association with an element clipping compositing descendants." },
+                    { "name": "perspective", "type": "boolean", "optional": true, "description": "Composition due to association with an element with perspective applied." },
+                    { "name": "preserve3D", "type": "boolean", "optional": true, "description": "Composition due to association with an element with a \"transform-style: preserve-3d\" style." },
+                    { "name": "root", "type": "boolean", "optional": true, "description": "Root layer." },
+                    { "name": "layerForClip", "type": "boolean", "optional": true, "description": "Layer for clip." },
+                    { "name": "layerForScrollbar", "type": "boolean", "optional": true, "description": "Layer for scrollbar."},
+                    { "name": "layerForScrollingContainer", "type": "boolean", "optional": true, "description": "Layer for scrolling container." },
+                    { "name": "layerForForeground", "type": "boolean", "optional": true, "description": "Layer for foreground." },
+                    { "name": "layerForBackground", "type": "boolean", "optional": true, "description": "Layer for background." },
+                    { "name": "layerForMask", "type": "boolean", "optional": true, "description": "Layer for mask." },
+                    { "name": "layerForVideoOverlay", "type": "boolean", "optional": true, "description": "Layer for video overlay." }
+                ]
+
             }
         ],
         "commands": [
             {
                 "name": "enable",
                 "description": "Enables compositing tree inspection."
             },
             {
                 "name": "disable",
                 "description": "Disables compositing tree inspection."
             },
             {
                 "name": "getLayers",
                 "parameters": [
                     { "name": "nodeId", "optional": true, "$ref": "DOM.NodeId", "description": "Root of the subtree for which we want to gather layers (return entire tree if not specified)" }
                 ],
                 "description": "Returns the layer tree structure of the current page.",
                 "returns": [
                     { "name": "layers", "type": "array", "items": { "$ref": "Layer" }, "description": "Child layers." }
                 ]
+            },
+            {
+                "name": "reasonsForCompositingLayer",

[pfeldman, 2013/08/22 16:49:54]

compositingReasons

+                "parameters": [
+                    { "name": "layerId", "$ref": "LayerId", "description": "The id of the layer for which we want to get the reasons it was composited." }
+                ],
+                "description": "Provides the reasons why the given layer was composited.",
+                "returns": [
+                    { "name": "compositingReasons", "$ref": "CompositingReasons", "description": "An object containing the reasons why the layer was composited as properties." }
+                ]
             }
         ],
         "events": [
             {
                 "name": "layerTreeDidChange"
             }
         ]
     },
     {
         "domain": "Tracing",
@@ skipping 17 matching lines @@
                 "parameters": [
                     { "name": "value", "type": "array", "items": { "type": "object" } }
                 ]
             },
             {
                 "name": "tracingComplete"
             }
         ]
     }]
 }