Fix for GH 158.

After computing the png image, the `model.setData` call was treating
plotly's traces array (`data`) as if it were the bundle's `data`
property (`model.data`).

This was causing a malformed bundle to be saved in the notebook,
and causing only the image/png form to be restored on notebook load.

Author: jonmmease

packages/plotly-extension/src/index.ts

@@ -62,7 +62,11 @@ export class RenderedPlotly extends Widget implements IRenderMime.IRenderer {
             height: this.node.offsetHeight
           }).then((url: string) => {
             const imageData = url.split(',')[1];
-            model.setData({ data: { ...data, 'image/png': imageData } });
+            if (model.data['image/png'] !== imageData) {
+              model.setData({
+                data: { ...model.data, 'image/png': imageData }
+              });
+            }
           });
         });
       }
@@ -73,7 +77,9 @@ export class RenderedPlotly extends Widget implements IRenderMime.IRenderer {
         height: this.node.offsetHeight
       }).then((url: string) => {
         const imageData = url.split(',')[1];
-        model.setData({ data: { ...data, 'image/png': imageData } });
+        if (model.data['image/png'] !== imageData) {
+          model.setData({ data: { ...model.data, 'image/png': imageData } });
+        }
       });
     });
   }