Add a Finch feature and runtime flag for multidevice.

chrome/browser/flag_descriptions.cc

Index: chrome/browser/flag_descriptions.cc
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index 27a963351a282e3426826dd9d3f41ea2e2e118bd..0deb3671bbe6d82a4a145eb6ff912b936c5baea2 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -3291,6 +3291,10 @@ const char kUiDevToolsDescription[] =
     "Enables inspection of native UI elements. For local inspection use "
     "chrome://inspect#other";
 
+const char kMultideviceName[] = "Enable multidevice features";
+const char kMultideviceDescription[] =
+    "Enables UI for controlling multidevice features.";
+
 #endif  // defined(OS_CHROMEOS)
 
 }  // namespace flag_descriptions