Bug 1155465 - part1: layout-view: use content-type CSS_VALUE for editors;r=miker

Inplace editors for the layout view should use the CSS_VALUE content-type since they
allow to edit a CSS value, and not just plain text.

MozReview-Commit-ID: 9mQA1fSmXvD

--HG--
extra : rebase_source : 952e83cc28a4a218f7b88f7bd7bb3b132aa1bc37

devtools/client/inspector/layout/layout.js

@@ -306,7 +306,10 @@ LayoutView.prototype = {
     let editor = new InplaceEditor({
       element: element,
       initial: initialValue,
-
+      contentType: InplaceEditor.CONTENT_TYPES.CSS_VALUE,
+      property: {
+        name: dimension.property
+      },
       start: self => {
         self.elt.parentNode.classList.add("layout-editing");
       },