DevTools: simplify setScriptSource and restartFrame return values

Source/core/inspector/InjectedScriptSource.js

Index: Source/core/inspector/InjectedScriptSource.js
diff --git a/Source/core/inspector/InjectedScriptSource.js b/Source/core/inspector/InjectedScriptSource.js
index 214b74400eeac3c0be8a4ccefb26af062c947a74..f8f2343b90c7cc38de1252244f155e73486e7bd5 100644
--- a/Source/core/inspector/InjectedScriptSource.js
+++ b/Source/core/inspector/InjectedScriptSource.js
@@ -959,10 +959,7 @@ InjectedScript.prototype = {
         var callFrame = this._callFrameForId(topCallFrame, callFrameId);
         if (!callFrame)
             return "Could not find call frame with given id";
-        var result = callFrame.restart();
-        if (result === false)
-            result = "Restart frame is not supported";
-        return result;
+        return callFrame.restart();
     },
 
     /**