DevTools: Don't show an error in npm start when CHROMIUM_PATH is missing

third_party/WebKit/Source/devtools/scripts/chrome_debug_launcher/launch_chrome.js

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 var childProcess = require("child_process");
 var fs = require("fs");
 var path = require("path");
 var shell = childProcess.execSync;
 
 var remoteDebuggingPort = parseInt(process.env.REMOTE_DEBUGGING_PORT, 10) || 9222;
@@ skipping 60 matching lines @@
 {
     console.log(`Launching Chrome from ${filePath}`);
     console.log("Chrome args:", chromeArgs.join(" "), "\n");
     var child;
     try {
         child = childProcess.spawn(filePath, chromeArgs, {
             stdio: "ignore",
         });
     } catch (error) {
         onLaunchChromeError();
+        if (cleanup)
+            cleanup();
+        return;
     }
     child.on("error", onLaunchChromeError);
     child.on("exit", onExit);
     function onExit(code)
     {
         if (cleanup)
             cleanup();
         console.log("Exited Chrome with code", code);
     }
 }
@@ skipping 15 matching lines @@
 {
     var string = buffer.toString();
     console.log(string);
     return string;
 }
 
 function shellOutput(command)
 {
     return shell(command).toString().trim();
 }