[ios] Wraps the QR scanner in a basic coordinator.

The new QRScannerCoordinator class provides a single entry point for the
activity services feature, including all of the necessary public API.
Dependencies on other components are encapsulated within new protocols that are
declared in the requirements/ subdirectory.

Bug: 
Change-Id: I532c78a3be95589e4651c210f80a4ae7bf4625e3
Reviewed-on: https://chromium-review.googlesource.com/577814
Reviewed-by: Mark Cogan <[email protected]>
Commit-Queue: Rohit Rao (ping after 24h) <[email protected]>
Cr-Commit-Position: refs/heads/master@{#494794}
diff --git a/ios/chrome/browser/ui/commands/BUILD.gn b/ios/chrome/browser/ui/commands/BUILD.gn
index 3f20de2..d165a0b 100644
--- a/ios/chrome/browser/ui/commands/BUILD.gn
+++ b/ios/chrome/browser/ui/commands/BUILD.gn
@@ -20,6 +20,7 @@
     "open_new_tab_command.mm",
     "open_url_command.h",
     "open_url_command.mm",
+    "qr_scanner_commands.h",
     "reading_list_add_command.h",
     "reading_list_add_command.mm",
     "show_mail_composer_command.h",