Add chrome://flags entry for per profile network contexts

In order to be confident this is safe to launch on ChromeOS, allow the
feature to be controlled by a chrome://flags entry, which will persist
across restarts independent of the Finch configuration.

Bug: 1049833
Change-Id: I9975722c694a5bda8de8e56f3c87e781883f3b3d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3046474
Reviewed-by: Bettina Dea <[email protected]>
Commit-Queue: Daniel Rubery <[email protected]>
Cr-Commit-Position: refs/heads/master@{#905435}
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index 476d354e..2acb200b 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -2186,6 +2186,12 @@
     "Enables the second set of privacy sandbox settings. Requires "
     "#privacy-sandbox-settings to also be enabled";
 
+const char kSafeBrowsingPerProfileNetworkContextsName[] =
+    "Per-profile Safe Browsing network contexts";
+const char kSafeBrowsingPerProfileNetworkContextsDescription[] =
+    "Keys the Safe Browsing network context by the profile initiating the "
+    "request";
+
 const char kSafetyCheckWeakPasswordsName[] = "Safety check for weak passwords";
 const char kSafetyCheckWeakPasswordsDescription[] =
     "If weak passwords were found, show them in safety check.";