Bug 1446222 - Move DevTools worker startup to new dir. r=jdescottes

Move and rename the server's worker debugger script that starts DevTools for a
worker from `worker.js` to `startup/worker.js`.

These code paths will likely change more as Site Isolation work continues, but
for now, we have this light cleanup to gather startup-related paths together.

MozReview-Commit-ID: EvzDSGnG1vU

--HG--
rename : devtools/server/worker.js => devtools/server/startup/worker.js
extra : rebase_source : e0b4600a0644e3e8ebb14f3da9c7dcea94d776ad

devtools/server/main.js

@@ -779,11 +779,15 @@ var DebuggerServer = {
     });
   },
 
+  /**
+   * Start a DevTools server in a worker and add it as a child server for an active
+   * connection.
+   */
   connectToWorker(connection, dbg, id, options) {
     return new Promise((resolve, reject) => {
       // Step 1: Ensure the worker debugger is initialized.
       if (!dbg.isInitialized) {
-        dbg.initialize("resource://devtools/server/worker.js");
+        dbg.initialize("resource://devtools/server/startup/worker.js");
 
         // Create a listener for rpc requests from the worker debugger. Only do
         // this once, when the worker debugger is first initialized, rather than

devtools/server/moz.build

@@ -19,7 +19,6 @@ XPCSHELL_TESTS_MANIFESTS += ['tests/unit/xpcshell.ini']
 
 DevToolsModules(
     'main.js',
-    'worker.js'
 )
 
 with Files('**'):

devtools/server/startup/moz.build

@@ -8,4 +8,5 @@ DevToolsModules(
     'content-process.js',
     'content-process.jsm',
     'frame.js',
+    'worker.js',
 )

devtools/server/startup/worker.js

@@ -7,6 +7,12 @@
 /* eslint-env mozilla/chrome-worker */
 /* global worker, loadSubScript, global */
 
+/*
+ * Worker debugger script that listens for requests to start a `DebuggerServer` for a
+ * worker in a process.  Loaded into a specific worker during
+ * `DebuggerServer.connectToWorker` which is called from the same process as the worker.
+ */
+
 // This function is used to do remote procedure calls from the worker to the
 // main thread. It is exposed as a built-in global to every module by the
 // worker loader. To make sure the worker loader can access it, it needs to be