DevTools: implement hidpi-friendly success/error/warning balls.

Source/devtools/front_end/RequestHeadersView.js

Index: Source/devtools/front_end/RequestHeadersView.js
diff --git a/Source/devtools/front_end/RequestHeadersView.js b/Source/devtools/front_end/RequestHeadersView.js
index 2e89fea2e48f01a43d7c5b8bc6b4532147b54ba8..33ade135ef76afa9d0a65148cb5b614be0a96690 100644
--- a/Source/devtools/front_end/RequestHeadersView.js
+++ b/Source/devtools/front_end/RequestHeadersView.js
@@ -374,22 +374,21 @@ WebInspector.RequestHeadersView.prototype = {
         statusCodeElement.hidden = !this._request.statusCode;
 
         if (this._request.statusCode) {
-            var statusImageSource = "";
+            var statusCodeFragment = document.createDocumentFragment();
+            statusCodeFragment.createChild("div", "header-name").textContent = WebInspector.UIString("Status Code") + ":";
+
+            var statusCodeImage = statusCodeFragment.createChild("div", "resource-status-image");
+            statusCodeImage.title = this._request.statusCode + " " + this._request.statusText;
+
             if (this._request.statusCode < 300 || this._request.statusCode === 304)
-                statusImageSource = "Images/successGreenDot.png";
+                statusCodeImage.addStyleClass("green-ball");
             else if (this._request.statusCode < 400)
-                statusImageSource = "Images/warningOrangeDot.png";
+                statusCodeImage.addStyleClass("orange-ball");
             else
-                statusImageSource = "Images/errorRedDot.png";
+                statusCodeImage.addStyleClass("red-ball");
 
             requestMethodElement.title = this._formatHeader(WebInspector.UIString("Request Method"), this._request.requestMethod);
 
-            var statusCodeFragment = document.createDocumentFragment();
-            statusCodeFragment.createChild("div", "header-name").textContent = WebInspector.UIString("Status Code") + ":";
-
-            var statusCodeImage = statusCodeFragment.createChild("img", "resource-status-image");
-            statusCodeImage.src = statusImageSource;
-            statusCodeImage.title = this._request.statusCode + " " + this._request.statusText;
             var value = statusCodeFragment.createChild("div", "header-value source-code");
             value.textContent = this._request.statusCode + " " + this._request.statusText;
             if (this._request.cached)