[pie] improvements to pie charts (apache#5236)

Pie chart was using `limit` instead of `row_limit` which didn't work.

Also set a lower default limit to 25 to prevent the chart from getting
super crowded.

Unrelated drive-by fix of setting "percentage metric" to default to `[]`

superset/assets/src/explore/controls.jsx

@@ -206,6 +206,7 @@ export const controls = {
   percent_metrics: {
     ...metrics,
     multi: true,
+    default: [],
     label: t('Percentage Metrics'),
     default: [],
     validators: [],
@@ -1447,6 +1448,16 @@ export const controls = {
     description: t('Whether to display the legend (toggles)'),
   },
 
+  show_labels: {
+    type: 'CheckboxControl',
+    label: t('Show Labels'),
+    renderTrigger: true,
+    default: true,
+    description: t(
+      'Whether to display the labels. Note that the label only displays when the the 5% ' +
+      'threshold.'),
+  },
+
   show_values: {
     type: 'CheckboxControl',
     label: t('Show Values'),

superset/assets/src/explore/visTypes.js

@@ -142,7 +142,7 @@ export const visTypes = {
           ['metric'],
           ['adhoc_filters'],
           ['groupby'],
-          ['limit'],
+          ['row_limit'],
         ],
       },
       {
@@ -151,11 +151,16 @@ export const visTypes = {
         controlSetRows: [
           ['pie_label_type'],
           ['donut', 'show_legend'],
-          ['labels_outside'],
+          ['show_labels', 'labels_outside'],
           ['color_scheme'],
         ],
       },
     ],
+    controlOverrides: {
+      row_limit: {
+        default: 25,
+      },
+    },
   },
 
   line: {

superset/assets/src/visualizations/nvd3_vis.js

@@ -272,6 +272,7 @@ export default function nvd3Vis(slice, payload) {
         if (fd.donut) {
           chart.donut(true);
         }
+        chart.showLabels(fd.show_labels);
         chart.labelsOutside(fd.labels_outside);
         chart.labelThreshold(0.05);  // Configure the minimum slice size for labels to show up
         if (fd.pie_label_type !== 'key_percent' && fd.pie_label_type !== 'key_value') {