Fetch SDCH dictionary as soon as current URL fetch completes

Rather than just waiting for 15 seconds, this patch fetches the
"suggested dicitionary" as soon as the current download completes.
This avoids stealing bandwidth from the original download, but 
works as quickly as possible to get the dictionary, so that the
user can receive compression results asap.

r=wtc
Review URL: http://codereview.chromium.org/20254

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@9597 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 7 insertions, 5 deletions

diff --git a/chrome/browser/net/sdch_dictionary_fetcher.cc b/chrome/browser/net/sdch_dictionary_fetcher.cc
index 5208f37..9bce5f3 100644
--- a/chrome/browser/net/sdch_dictionary_fetcher.cc
+++ b/chrome/browser/net/sdch_dictionary_fetcher.cc
@@ -18,8 +18,6 @@ void SdchDictionaryFetcher::Schedule(const GURL& dictionary_url) {
   ScheduleDelayedRun();
 }
 
-// TODO(jar): If QOS low priority is supported, switch to using that instead of
-// just waiting to do the fetch.
 void SdchDictionaryFetcher::ScheduleDelayedRun() {
   if (fetch_queue_.empty() || current_fetch_.get() || task_is_pending_)
     return;
diff --git a/chrome/browser/net/sdch_dictionary_fetcher.h b/chrome/browser/net/sdch_dictionary_fetcher.h
index b943a24..a0a9e2f 100644
--- a/chrome/browser/net/sdch_dictionary_fetcher.h
+++ b/chrome/browser/net/sdch_dictionary_fetcher.h
@@ -13,6 +13,7 @@
 #include <string>
 
 #include "base/compiler_specific.h"
+#include "base/scoped_ptr.h"
 #include "base/task.h"
 #include "chrome/browser/net/url_fetcher.h"
 #include "net/base/sdch_manager.h"
@@ -20,7 +21,7 @@
 class SdchDictionaryFetcher : public URLFetcher::Delegate,
                               public SdchFetcher {
  public:
-  SdchDictionaryFetcher() : 
+  SdchDictionaryFetcher() :
       ALLOW_THIS_IN_INITIALIZER_LIST(method_factory_(this)),
       task_is_pending_(false) {}
   virtual ~SdchDictionaryFetcher() {}
@@ -31,8 +32,11 @@ class SdchDictionaryFetcher : public URLFetcher::Delegate,
   virtual void Schedule(const GURL& dictionary_url);
 
  private:
-  // Delay between Schedule and actual download.
-  static const int kMsDelayFromRequestTillDownload = 15000;
+  // Delay in ms between Schedule and actual download.
+  // This leaves the URL in a queue, which is de-duped, so that there is less
+  // chance we'll try to load the same URL multiple times when a pile of
+  // page subresources (or tabs opened in parallel) all suggest the dictionary.
+  static const int kMsDelayFromRequestTillDownload = 100;
 
   // Ensure the download after the above delay.
   void ScheduleDelayedRun();