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/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 9aa0d60..6a15105 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1192,6 +1192,9 @@
 extern const char kWalletServiceUseSandboxName[];
 extern const char kWalletServiceUseSandboxDescription[];
 
+extern const char kWebBluetoothNewPermissionsBackendName[];
+extern const char kWebBluetoothNewPermissionsBackendDescription[];
+
 extern const char kWebBundlesName[];
 extern const char kWebBundlesDescription[];