DevTools: fix front-end compilation following r196255

Source/devtools/front_end/devtools.js

Index: Source/devtools/front_end/devtools.js
diff --git a/Source/devtools/front_end/devtools.js b/Source/devtools/front_end/devtools.js
index 8151833e2b59a4d464507c82b972fe41e812fa9b..746ec801fbc43e5d998485df756b812ad9370289 100644
--- a/Source/devtools/front_end/devtools.js
+++ b/Source/devtools/front_end/devtools.js
@@ -804,7 +804,12 @@ function installBackwardsCompatibility()
 
     // Support for legacy (<M41) frontends. Remove in M45.
     window.CSSStyleDeclaration.prototype.getPropertyCSSValue = getValue;
-    window.CSSPrimitiveValue = { CSS_PX: "CSS_PX" };
+
+    function CSSPrimitiveValue()
+    {
+    }
+    CSSPrimitiveValue.CSS_PX = 5;
+    window.CSSPrimitiveValue = CSSPrimitiveValue;
 
     // Support for legacy (<M44) frontends. Remove in M48.
     var styleElement = window.document.createElement("style");