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

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 9caa41c905668370c3147c1a5e51b5cfe0340970..44ac3e4fcd4b3ee40c5934255e97b14ca227eac9 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -273,6 +273,13 @@ const Experiment kExperiments[] = {
     kOsWin | kOsLinux,
     SINGLE_VALUE_TYPE(switches::kInstantAutocompleteImmediately)
   },
+  {
+    "block-reading-third-party-cookies",
+    IDS_FLAGS_BLOCK_ALL_THIRD_PARTY_COOKIES_NAME,
+    IDS_FLAGS_BLOCK_ALL_THIRD_PARTY_COOKIES_DESCRIPTION,
+    kOsAll,
+    SINGLE_VALUE_TYPE(switches::kBlockReadingThirdPartyCookies)
+  },
 };
 
 const Experiment* experiments = kExperiments;