add hoverlabel attribute container for all traces

- allow arrayOk for all hover label attribute
- don't set dflt for bgcolor, bordercolor and font.color
  as their value depends and the trace color and plot bgcolor

Author: etpinard

src/plots/attributes.js

@@ -8,6 +8,9 @@
 
 'use strict';
 
+var constants = require('./cartesian/constants');
+var fontAttrs = require('./font_attributes');
+var extendFlat = require('../lib/extend').extendFlat;
 
 module.exports = {
     type: {
@@ -80,6 +83,37 @@ module.exports = {
             'But, if `none` is set, click and hover events are still fired.'
         ].join(' ')
     },
+    hoverlabel: {
+        bgcolor: {
+            valType: 'color',
+            role: 'style',
+            arrayOk: true,
+            description: [
+                'Sets the background color of the hover label.'
+            ].join(' ')
+        },
+        bordercolor: {
+            valType: 'color',
+            role: 'style',
+            arrayOk: true,
+            description: [
+                'Sets the border color of the hover label.'
+            ].join(' ')
+        },
+        font: {
+            family: extendFlat({}, fontAttrs.family, {
+                arrayOk: true,
+                dflt: constants.HOVERFONT
+            }),
+            size: extendFlat({}, fontAttrs.size, {
+                arrayOk: true,
+                dflt: constants.HOVERFONTSIZE
+            }),
+            color: extendFlat({}, fontAttrs.color, {
+                arrayOk: true
+            })
+        }
+    },
     stream: {
         token: {
             valType: 'string',

src/plots/plots.js

@@ -811,6 +811,10 @@ plots.supplyTraceDefaults = function(traceIn, traceOutIndex, layout, traceInInde
         // gets overwritten in pie, geo and ternary modules
         coerce('hoverinfo', (layout._dataLength === 1) ? 'x+y+z+text' : undefined);
 
+        coerce('hoverlabel.bgcolor');
+        coerce('hoverlabel.bordercolor');
+        Lib.coerceFont(coerce, 'hoverlabel.font');
+
         // TODO add per-base-plot-module trace defaults step
 
         if(_module) _module.supplyDefaults(traceIn, traceOut, defaultColor, layout);