Adds custom ttl argument to HostCache::Set.

net/base/host_cache.h

Index: net/base/host_cache.h
diff --git a/net/base/host_cache.h b/net/base/host_cache.h
index 62c07ab978f51ee76132809e70b16eacea79aa8b..394736c962d287f9cf576ad82dbc9137dab35149 100644
--- a/net/base/host_cache.h
+++ b/net/base/host_cache.h
@@ -88,8 +88,16 @@ class NET_EXPORT HostCache : NON_EXPORTED_BASE(public base::NonThreadSafe) {
 
   // Overwrites or creates an entry for |key|. Returns the pointer to the
   // entry, or NULL on failure (fails if caching is disabled).
-  // (|error|, |addrlist|) is the value to set, and |now| is the current
-  // timestamp.
+  // (|error|, |addrlist|) is the value to set, |ttl| is the "time to live",

[cbentzel, 2012/01/13 01:06:14]

How much work would it be to only allow this version of Set and not have the ttl
== 0 be equivalent to "use the default"?

I wonder because DNS TTLs of 0 are potentially allowed. It would also make the
API easier - could remove the defaults in the constructor, and the description
of what |ttl| represents becomes clearer.

[szym, 2012/01/14 16:30:54]

(Excluding unittests) There are three calls to HostCache::Set:
1) HostResolverImpl::OnJobComplete
2) AsyncHostResolver::OnDnsRequestComplete
3) (ProxyResolverJSBindings) DefaultJSBindings::DnsResolveHelper

There are two calls to HostCache::HostCache where the default TTL values are
set:
1) HostCache::CreateDefaultCache // success: 1 min, failure: 0
2) ProxyResolverV8::GetProxyURL  // success: 5 min, failure: 5 min

So we could easily move the default TTL values from HostCache to the sites
calling HostCache::Set. 

Regarding the other issue, entries with TTLs of 0 will never be returned by
HostCache::Lookup, so the only benefit of storing such entries afaik is
net-internals, even though they won't survive for long if the cache is at
capacity.

+  // and |now| is the current timestamp. If |ttl| is zero, the default,
+  // |success_entry_ttl| or |failure_entry_ttl| is used.
+  Entry* Set(const Key& key,
+             int error,
+             const AddressList& addrlist,
+             base::TimeDelta ttl,
+             base::TimeTicks now);
+
+  // Same as |Set(key, error, addrlist, TimeDelta(), now)|.
   Entry* Set(const Key& key,
              int error,
              const AddressList& addrlist,