Cleanup NavigationLoaderOnUI comments.

NavigationLoaderOnUI landed. Some comments about it are still there.
This patch remove them.

This disambiguate the fact this variable can be safely used:
NavigationURLLoaderImpl::URLLoaderRequestController::browser_context_

Bug: 824840
Change-Id: Icb6dc5050a604878531958acbc0fdc2a7739d420
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2120717
Auto-Submit: Arthur Sonzogni <arthursonzogni@chromium.org>
Commit-Queue: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#753552}

content/browser/loader/cross_origin_read_blocking_checker.cc

@@ -18,9 +18,9 @@
 
 namespace content {
 
-// When NavigationLoaderOnUI is enabled, the CrossOriginReadBlockingChecker
-// lives on the UI thread, but blobs must be read on IO. This class handles all
-// blob access for CrossOriginReadBlockingChecker.
+// The CrossOriginReadBlockingChecker lives on the UI thread, but blobs must be
+// read on IO. This class handles all blob access for
+// CrossOriginReadBlockingChecker.
 class CrossOriginReadBlockingChecker::BlobIOState {
  public:
   BlobIOState(base::WeakPtr<CrossOriginReadBlockingChecker> checker,

content/browser/loader/navigation_url_loader_impl.cc

@@ -1242,7 +1242,6 @@ class NavigationURLLoaderImpl::URLLoaderRequestController
   // Counts the time overhead of all the hops from the UI to the IO threads.
   base::TimeDelta ui_to_io_time_;
 
-  // Only used when NavigationLoaderOnUI is enabled:
   BrowserContext* browser_context_;
 
   network::mojom::URLResponseHeadPtr head_;