Clarify wording around blocking 3rd party cookies and add lab to block reading of 3rd party cookies

net/base/static_cookie_policy.cc

Index: net/base/static_cookie_policy.cc
diff --git a/net/base/static_cookie_policy.cc b/net/base/static_cookie_policy.cc
index 0ff6ead91e284ae7be284902badca1a44cbc2121..19e0a16028255aff66c90c980dd4bdb5554b52ad 100644
--- a/net/base/static_cookie_policy.cc
+++ b/net/base/static_cookie_policy.cc
@@ -16,9 +16,13 @@ int StaticCookiePolicy::CanGetCookies(const GURL& url,
                                       CompletionCallback* callback) {
   switch (type_) {
     case StaticCookiePolicy::ALLOW_ALL_COOKIES:
+    case StaticCookiePolicy::BLOCK_SETTING_THIRD_PARTY_COOKIES:
       return OK;
-    case StaticCookiePolicy::BLOCK_THIRD_PARTY_COOKIES:
-      return OK;
+    case StaticCookiePolicy::BLOCK_ALL_THIRD_PARTY_COOKIES:
+      if (first_party_for_cookies.is_empty())
+        return OK;  // Empty first-party URL indicates a first-party request.
+      return RegistryControlledDomainService::SameDomainOrHost(
+          url, first_party_for_cookies) ? OK : ERR_ACCESS_DENIED;
     case StaticCookiePolicy::BLOCK_ALL_COOKIES:
       return ERR_ACCESS_DENIED;
     default:
@@ -34,7 +38,8 @@ int StaticCookiePolicy::CanSetCookie(const GURL& url,
   switch (type_) {
     case StaticCookiePolicy::ALLOW_ALL_COOKIES:
       return OK;
-    case StaticCookiePolicy::BLOCK_THIRD_PARTY_COOKIES:
+    case StaticCookiePolicy::BLOCK_SETTING_THIRD_PARTY_COOKIES:
+    case StaticCookiePolicy::BLOCK_ALL_THIRD_PARTY_COOKIES:
       if (first_party_for_cookies.is_empty())
         return OK;  // Empty first-party URL indicates a first-party request.
       return RegistryControlledDomainService::SameDomainOrHost(