Support for json media types as (non-image) mime types.

Source/devtools/front_end/RequestPreviewView.js

Index: Source/devtools/front_end/RequestPreviewView.js
diff --git a/Source/devtools/front_end/RequestPreviewView.js b/Source/devtools/front_end/RequestPreviewView.js
index 8ff81514906112805c884c03b3067a479e3fcfea..0e94dba44924f91f6c66d5d0c9c29f30da3c7148 100644
--- a/Source/devtools/front_end/RequestPreviewView.js
+++ b/Source/devtools/front_end/RequestPreviewView.js
@@ -83,7 +83,8 @@ WebInspector.RequestPreviewView.prototype = {
     _createPreviewView: function()
     {
         if (this.request.content) {
-            if (this.request.mimeType === "application/json") {
+            var jsonMediaTypeRE = /^application\/[^;]*\+json/;
+            if (this.request.mimeType === "application/json" || jsonMediaTypeRE.test(this.request.mimeType)) {
                 var jsonView = this._jsonView();
                 if (jsonView)
                     return jsonView;