Fix #820 (#821)

* Add test for inlineStyles plugin/CSSStyleDeclaration API.

* Adjust test.

* Always initialize element attrs with empty object.
Improve code.

lib/svgo/css-style-declaration.js

@@ -18,11 +18,6 @@ var CSSStyleDeclaration = function(node) {
 
 
 CSSStyleDeclaration.prototype.hasStyle = function() {
-    this.styleAttr = { // empty style attr
-        'name': 'style',
-        'value': null
-    };
-
     this.addStyleHandler();
 };
 
@@ -33,6 +28,11 @@ CSSStyleDeclaration.prototype.hasStyle = function() {
 
 CSSStyleDeclaration.prototype.addStyleHandler = function() {
 
+    this.styleAttr = { // empty style attr
+        'name': 'style',
+        'value': null
+    };
+
     Object.defineProperty(this.parentNode.attrs, 'style', {
         get: this.getStyleAttr.bind(this),
         set: this.setStyleAttr.bind(this),

lib/svgo/svg2js.js

@@ -87,15 +87,14 @@ module.exports = function(data, callback) {
         var elem = {
             elem: data.name,
             prefix: data.prefix,
-            local: data.local
+            local: data.local,
+            attrs: {}
         };
+
         elem.class = new CSSClassList(elem);
         elem.style = new CSSStyleDeclaration(elem);
 
         if (Object.keys(data.attributes).length) {
-            elem.attrs = {};
-
-
             for (var name in data.attributes) {
 
                 if (name === 'class') { // has class attribute