browser(firefox): do not double-attach session to the same target (#4027)

We currently might double-attach to the target in `BrowserHandler` since we iterate over all targets, and then subscribe to the additional event when target is getting initialized.

This patch fixes this race condition and should unblock the roll to r1177.

References #3995

Author: aslushnikov

browser_patches/firefox/BUILD_NUMBER

@@ -1,2 +1,2 @@
-1177
-Changed: [email protected] Wed Sep 30 03:11:29 MDT 2020
+1178
+Changed: [email protected] Wed Sep 30 23:36:27 PDT 2020

browser_patches/firefox/juggler/TargetRegistry.js

@@ -147,8 +147,8 @@ class TargetRegistry {
 
         const sessions = [];
         const readyData = { sessions, target };
-        this.emit(TargetRegistry.Events.TargetCreated, readyData);
         target.markAsReported();
+        this.emit(TargetRegistry.Events.TargetCreated, readyData);
         return {
           scriptsToEvaluateOnNewDocument: target.browserContext().scriptsToEvaluateOnNewDocument,
           bindings: target.browserContext().bindings,
@@ -321,8 +321,8 @@ class TargetRegistry {
     return target.id();
   }
 
-  targets() {
-    return Array.from(this._browserToTarget.values());
+  reportedTargets() {
+    return Array.from(this._browserToTarget.values()).filter(pageTarget => pageTarget._isReported);
   }
 
   targetForBrowser(browser) {
@@ -364,6 +364,7 @@ class PageTarget {
       helper.addProgressListener(tab.linkedBrowser, navigationListener, Ci.nsIWebProgress.NOTIFY_LOCATION),
     ];
 
+    this._isReported = false;
     this._reportedPromise = new Promise(resolve => {
       this._reportedCallback = resolve;
     });
@@ -379,6 +380,7 @@ class PageTarget {
   }
 
   markAsReported() {
+    this._isReported = true;
     this._reportedCallback();
   }
 
@@ -491,7 +493,8 @@ class PageTarget {
     this._registry._browserToTarget.delete(this._linkedBrowser);
     this._registry._browserBrowsingContextToTarget.delete(this._linkedBrowser.browsingContext);
     helper.removeListeners(this._eventListeners);
-    this._registry.emit(TargetRegistry.Events.TargetDestroyed, this);
+    if (this._isReported)
+      this._registry.emit(TargetRegistry.Events.TargetDestroyed, this);
   }
 }
 

browser_patches/firefox/juggler/content/main.js

@@ -90,10 +90,11 @@ const applySetting = {
 };
 
 function initialize() {
-  const loadContext = docShell.QueryInterface(Ci.nsILoadContext);
-  const userContextId = loadContext.originAttributes.userContextId;
-
-  const response = sendSyncMessage('juggler:content-ready', { userContextId })[0];
+  const response = sendSyncMessage('juggler:content-ready')[0];
+  // If we didn't get a response, then we don't want to do anything
+  // as a part of this frame script.
+  if (!response)
+    return;
   const {
     sessionIds = [],
     scriptsToEvaluateOnNewDocument = [],

browser_patches/firefox/juggler/protocol/BrowserHandler.js

@@ -29,7 +29,7 @@ class BrowserHandler {
     this._enabled = true;
     this._attachToDefaultContext = attachToDefaultContext;
 
-    for (const target of this._targetRegistry.targets()) {
+    for (const target of this._targetRegistry.reportedTargets()) {
       if (!this._shouldAttachToTarget(target))
         continue;
       const session = this._dispatcher.createSession();