Bug 1654124, switch to get the remote type from the browsing context rather than the message manager in a few places, r=mconley

Differential Revision: https://phabricator.services.mozilla.com/D84269

browser/base/content/tabbrowser.js

@@ -2613,7 +2613,8 @@
               preferredRemoteType
             );
         if (sameProcessAsFrameLoader) {
-          remoteType = sameProcessAsFrameLoader.messageManager.remoteType;
+          remoteType =
+            sameProcessAsFrameLoader.browsingContext.currentRemoteType;
         }
 
         // If we open a new tab with the newtab URL in the default

browser/components/newtab/test/browser/abouthomecache/head.js

@@ -79,8 +79,7 @@ async function simulateRestart(
   }
 ) {
   info("Simulating restart of the browser");
-  let processManager = browser.messageManager.processMessageManager;
-  if (processManager.remoteType !== E10SUtils.PRIVILEGEDABOUT_REMOTE_TYPE) {
+  if (browser.remoteType !== E10SUtils.PRIVILEGEDABOUT_REMOTE_TYPE) {
     throw new Error(
       "prepareLoadFromCache should only be called on a browser " +
         "loaded in the privileged about content process."
@@ -109,6 +108,7 @@ async function simulateRestart(
   AboutHomeStartupCache.init();
 
   if (AboutHomeStartupCache.initted) {
+    let processManager = browser.messageManager.processMessageManager;
     AboutHomeStartupCache.sendCacheInputStreams(processManager);
 
     info("Waiting for AboutHomeStartupCache cache entry");

toolkit/content/widgets/browser-custom-element.js

@@ -495,11 +495,7 @@
     }
 
     get remoteType() {
-      if (!this.isRemoteBrowser || !this.messageManager) {
-        return null;
-      }
-
-      return this.messageManager.remoteType;
+      return this.browsingContext?.currentRemoteType;
     }
 
     get isCrashed() {