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 d5237e05bf1d7bebec47a6e31b7b975eea7241fb..c9eb937e40d63464a6dc3be00f46236f3f1fd654 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;