browser(firefox): move user agent emulation to browser side (#4016)

References #3995

browser_patches/firefox/BUILD_NUMBER

@@ -1,2 +1,2 @@
-1176
-Changed: lushnikov@chromium.org Wed Sep 30 03:06:09 MDT 2020
+1177
+Changed: lushnikov@chromium.org Wed Sep 30 03:11:29 MDT 2020

browser_patches/firefox/juggler/TargetRegistry.js

@@ -175,6 +175,7 @@ class TargetRegistry {
       if (!browserContext)
         throw new Error(`Internal error: cannot find context for userContextId=${userContextId}`);
       const target = new PageTarget(this, window, tab, browserContext, openerTarget);
+      target.updateUserAgent();
       if (!hasExplicitSize)
         target.updateViewportSize();
     };
@@ -393,6 +394,10 @@ class PageTarget {
     return this._browserContext;
   }
 
+  updateUserAgent() {
+    this._linkedBrowser.browsingContext.customUserAgent = this._browserContext.defaultUserAgent;
+  }
+
   async updateViewportSize() {
     // Viewport size is defined by three arguments:
     // 1. default size. Could be explicit if set as part of `window.open` call, e.g.
@@ -513,6 +518,7 @@ class BrowserContext {
     this.ignoreHTTPSErrors = undefined;
     this.downloadOptions = undefined;
     this.defaultViewportSize = undefined;
+    this.defaultUserAgent = null;
     this.screencastOptions = undefined;
     this.scriptsToEvaluateOnNewDocument = [];
     this.bindings = [];
@@ -559,6 +565,12 @@ class BrowserContext {
     }
   }
 
+  async setDefaultUserAgent(userAgent) {
+    this.defaultUserAgent = userAgent;
+    for (const page of this.pages)
+      page.updateUserAgent();
+  }
+
   async setDefaultViewport(viewport) {
     this.defaultViewportSize = viewport ? viewport.viewportSize : undefined;
     const promises = Array.from(this.pages).map(page => page.updateViewportSize());

browser_patches/firefox/juggler/content/main.js

@@ -59,10 +59,6 @@ const applySetting = {
         Ci.nsIDocShell.ONLINE_OVERRIDE_ONLINE : Ci.nsIDocShell.ONLINE_OVERRIDE_OFFLINE;
   },
 
-  userAgent: (userAgent) => {
-    docShell.browsingContext.customUserAgent = userAgent;
-  },
-
   bypassCSP: (bypassCSP) => {
     docShell.bypassCSPEnabled = bypassCSP;
   },

browser_patches/firefox/juggler/protocol/BrowserHandler.js

@@ -197,7 +197,7 @@ class BrowserHandler {
   }
 
   async setUserAgentOverride({browserContextId, userAgent}) {
-    await this._targetRegistry.browserContextForId(browserContextId).applySetting('userAgent', nullToUndefined(userAgent));
+    await this._targetRegistry.browserContextForId(browserContextId).setDefaultUserAgent(userAgent);
   }
 
   async setBypassCSP({browserContextId, bypassCSP}) {