Don't create promise or invoke onload for data uri images

 - Stash prior input image src string as the this._imgSrc property
 - Pull datauti code outside of the promise, so that we skip creating
 the promise and skip creating an Image() object, and skip running the
 onload function.

Author: jonmmease

Diff for: src/components/images/draw.js

@@ -74,21 +74,20 @@ module.exports = function draw(gd) {
     function setImage(d) {
         var thisImage = d3.select(this);
 
-        if(this.img && this.img.src === d.source) {
+        if(this._imgSrc === d.source) {
             return;
         }
 
         thisImage.attr('xmlns', xmlnsNamespaces.svg);
 
-        var imagePromise = new Promise(function(resolve) {
-            var img = new Image();
-            this.img = img;
+        if(d.source && d.source.slice(0, 5) === 'data:') {
+            thisImage.attr('xlink:href', d.source);
+            this._imgSrc = d.source;
+        } else {
+            var imagePromise = new Promise(function(resolve) {
+                var img = new Image();
+                this.img = img;
 
-            if(d.source && d.source.slice(0, 5) === 'data:') {
-                img.src = d.source;
-                thisImage.attr('xlink:href', d.source);
-                resolve();
-            } else {
                 // If not set, a `tainted canvas` error is thrown
                 img.setAttribute('crossOrigin', 'anonymous');
                 img.onerror = errorHandler;
@@ -110,19 +109,19 @@ module.exports = function draw(gd) {
                     resolve();
                 };
 
-
                 thisImage.on('error', errorHandler);
 
                 img.src = d.source;
-            }
+                this._imgSrc = d.source;
 
-            function errorHandler() {
-                thisImage.remove();
-                resolve();
-            }
-        }.bind(this));
+                function errorHandler() {
+                    thisImage.remove();
+                    resolve();
+                }
+            }.bind(this));
 
-        gd._promises.push(imagePromise);
+            gd._promises.push(imagePromise);
+        }
     }
 
     function applyAttributes(d) {