Add about flag for Previews coin flip

Bug: 1000431
Change-Id: I384efcd3fc30de6723bdaf777763b4bfb4291695
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1783111
Reviewed-by: Tarun Bansal <[email protected]>
Commit-Queue: Robert Ogden <[email protected]>
Cr-Commit-Position: refs/heads/master@{#692885}
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index ffd8dcb..82c3fa6 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -670,6 +670,10 @@
     "This requires enable-lite-page-server-previews to be enabled along with "
     "network-service.";
 
+const char kEnablePreviewsCoinFlipName[] = "Enable Previews Coin Flip";
+const char kEnablePreviewsCoinFlipDescription[] =
+    "Enable coin flip experimentation of Previews.";
+
 const char kBuiltInModuleAllName[] = "All experimental built-in modules";
 const char kBuiltInModuleAllDescription[] =
     "Enable all experimental built-in modules, as well as built-in module "