Clean up dns prefetch code, and also port it.

- remove slave threads and use HostResolver in asynchronous mode instead (while still limiting number of concurrent lookups)

- make the implementation portable and make DnsMaster unit test compile and pass on Linux

- add more tests to DnsMaster unit test to simulate various shutdown scenarios, concurrent lookups, and to verify that we don't exceed our limit of concurrent lookup requests)

- remove some tests which relied on specifics of slaves' inner working

- adjust initialization and shutdown of dns prefetching (now it relies on the IO message loop being present)

Bonus: shutdown is almost instant now, no need to have a timeout.

BUG=5687, 6683

Review URL: http://codereview.chromium.org/15076

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@10021 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 12 insertions, 2 deletions

diff --git a/chrome/browser/net/dns_global.h b/chrome/browser/net/dns_global.h
index 2ba0e70..80cf6ff 100644
--- a/chrome/browser/net/dns_global.h
+++ b/chrome/browser/net/dns_global.h
@@ -19,10 +19,17 @@ class PrefService;
 
 namespace chrome_browser_net {
 
-// Functions to initialize our global state so that PrefetchDns() can be called.
+// Initialize dns prefetching subsystem. Must be called before any other
+// functions.
 void InitDnsPrefetch(PrefService* user_prefs);
+
+// Cancel pending lookup requests and don't make new ones.
 void ShutdownDnsPrefetch();
 
+// Free all resources allocated by InitDnsPrefetch. After that you must not call
+// any function from this file.
+void FreeDnsPrefetchResources();
+
 //------------------------------------------------------------------------------
 // Global APIs relating to Prefetching in browser
 void EnableDnsPrefetch(bool enable);
@@ -53,7 +60,10 @@ class DnsPrefetcherInit {
   explicit DnsPrefetcherInit(PrefService* user_prefs) {
     InitDnsPrefetch(user_prefs);
   }
-  ~DnsPrefetcherInit() {ShutdownDnsPrefetch();}
+
+  ~DnsPrefetcherInit() {
+    FreeDnsPrefetchResources();
+  }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DnsPrefetcherInit);