Simplify CookieMonster::SetAllCookies{,Async}() implementation.

net/cookies/cookie_monster.h

Index: net/cookies/cookie_monster.h
diff --git a/net/cookies/cookie_monster.h b/net/cookies/cookie_monster.h
index fe968dba700b051fb1d4cddd81dd2ea6d54159ca..0136d5bc0f70f4af2c7c9d2ee38579d75341ccac 100644
--- a/net/cookies/cookie_monster.h
+++ b/net/cookies/cookie_monster.h
@@ -149,8 +149,8 @@ class NET_EXPORT CookieMonster : public CookieStore {
 
   ~CookieMonster() override;
 
-  // Writes all the cookies in |list| into the store, replacing existing
-  // cookies that collide.  Does not affect cookies not listed in |list|.
+  // Writes all the cookies in |list| into the store, replacing all cookies
+  // currently present in store.
   // This method does not flush the backend.
   // TODO(rdsmith, mmenke): Do not use this function; it is deprecated
   // and should be removed.