BundledExchanges: prepare to load BundledExchanges on response hook

This patch prepares to allow loading BundledExchanges source on
navigating to any URL. BundledExchangesHandle is now always
constructed on each navigation regardless of a valid
BundledExchangesSource presence if the kBundledHTTPExchanges
feature is enabled.

Bug: 966753
Change-Id: If6ff98c2e8ccf9cf70c24ed5fa9ea17a192d68de
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1736428
Reviewed-by: Kunihiko Sakamoto <[email protected]>
Reviewed-by: Scott Violet <[email protected]>
Reviewed-by: Tsuyoshi Horo <[email protected]>
Reviewed-by: Kinuko Yasuda <[email protected]>
Commit-Queue: Takashi Toyoshima <[email protected]>
Cr-Commit-Position: refs/heads/master@{#687623}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index b119845..7d7f851 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -4329,6 +4329,10 @@
      flag_descriptions::kDnsOverHttpsDescription, kOsAll,
      FEATURE_VALUE_TYPE(features::kDnsOverHttps)},
 
+    {"bundled-exchanges", flag_descriptions::kBundledHTTPExchangesName,
+     flag_descriptions::kBundledHTTPExchangesDescription, kOsAll,
+     FEATURE_VALUE_TYPE(features::kBundledHTTPExchanges)},
+
     // NOTE: Adding a new flag requires adding a corresponding entry to enum
     // "LoginCustomFlags" in tools/metrics/histograms/enums.xml. See "Flag
     // Histograms" in tools/metrics/histograms/README.md (run the