Add a flag for enabling WebXR AR module features

Moves the 'immersive-ar' session mode and environmentBlendMode attrib
behind this flag. (Was previously behind the WebXRHitTest flag.)

Bug: 994830
Change-Id: I3ed8e25ea0cc7abe0e3dc9fe4e3515662333cbc5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1758542
Commit-Queue: Brandon Jones <[email protected]>
Reviewed-by: Kentaro Hara <[email protected]>
Reviewed-by: Alex Moshchuk <[email protected]>
Reviewed-by: Brian Sheedy <[email protected]>
Reviewed-by: Alexander Cooper <[email protected]>
Reviewed-by: David Dorwin <[email protected]>
Reviewed-by: Mounir Lamouri <[email protected]>
Cr-Commit-Position: refs/heads/master@{#689083}
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index 8999500..745b1647 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -2144,6 +2144,11 @@
     "Enables access to experimental APIs to interact with Virtual Reality (VR) "
     "and Augmented Reality (AR) devices.";
 
+const char kWebXrArModuleName[] = "WebXR AR Module";
+const char kWebXrArModuleDescription[] =
+    "Enables access to Augmented Reality features defined in the WebXR AR "
+    "Module";
+
 const char kWebXrAnchorsName[] = "WebXR Anchors";
 const char kWebXrAnchorsDescription[] =
     "Enables access to anchors via WebXR API.";