DevTools: Provide #sourceURL for CSS stylesheets in the debug_devtools=1 mode

Source/devtools/front_end/Runtime.js

Index: Source/devtools/front_end/Runtime.js
diff --git a/Source/devtools/front_end/Runtime.js b/Source/devtools/front_end/Runtime.js
index 4003c80a197dfad1c9155805dc35fa332a769c4e..d35021651be84d1a3ddfca3732f32879e515704d 100644
--- a/Source/devtools/front_end/Runtime.js
+++ b/Source/devtools/front_end/Runtime.js
@@ -681,7 +681,11 @@ Runtime.Module.prototype = {
                 console.error("Failed to load stylesheet: " + path);
                 return;
             }
-            Runtime.cachedResources[path] = content;
+            var sourceURL = window.location.href;
+            if (window.location.search)
+                sourceURL.replace(window.location.search, "");
+            sourceURL = sourceURL.substring(0, sourceURL.lastIndexOf("/") + 1) + path;
+            Runtime.cachedResources[path] = content + "\n/*# sourceURL=" + sourceURL + " */";
         }
     },