Use BluetoothChooserContext behind flag

This change allows the permissions for Web Bluetooth to go through the
BluetoothChooserContext when NewWebBluetoothPermissionsBackend is
enabled. Since the Web Bluetooth API implementation is in content/ a
delegate class is required to allow WebBluetoothServiceImpl to access
the BluetoothChooserContext in chrome/.

Design doc:
https://docs.google.com/document/d/1h3uAVXJARHrNWaNACUPiQhLt7XI-fFFQoARSs1WgMDM/edit?usp=sharing

Bug: 589228

Change-Id: Ie95bd78368d9891168a50c280ca06dd0d8feff9d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1949530
Commit-Queue: Ovidio de Jesús Ruiz-Henríquez <[email protected]>
Reviewed-by: Charlie Reis <[email protected]>
Reviewed-by: Reilly Grant <[email protected]>
Cr-Commit-Position: refs/heads/master@{#739192}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 1a24f731..4ab1d3a 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1960,6 +1960,11 @@
          "1",
          autofill::switches::kWalletServiceUseSandbox,
          "0")},
+    {"enable-web-bluetooth-new-permissions-backend",
+     flag_descriptions::kWebBluetoothNewPermissionsBackendName,
+     flag_descriptions::kWebBluetoothNewPermissionsBackendDescription,
+     kOsAndroid | kOsDesktop,
+     FEATURE_VALUE_TYPE(features::kWebBluetoothNewPermissionsBackend)},
 #if defined(USE_AURA) || defined(OS_ANDROID)
     {"overscroll-history-navigation",
      flag_descriptions::kOverscrollHistoryNavigationName,