Http cache: Measure back navigations on the infinite cache simulation.

net/http/http_cache_transaction.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/http/http_cache_transaction.h"
 
 #include "build/build_config.h"
 
 #if defined(OS_POSIX)
 #include <unistd.h>
@@ skipping 246 matching lines @@
     return ERR_UNEXPECTED;
 
   SetRequest(net_log, request);
   if (infinite_cache_transaction_.get()) {
     if ((effective_load_flags_ & LOAD_BYPASS_CACHE) ||
         (effective_load_flags_ & LOAD_ONLY_FROM_CACHE) ||
         (effective_load_flags_ & LOAD_DISABLE_CACHE) ||
         (effective_load_flags_ & LOAD_VALIDATE_CACHE) ||
         (effective_load_flags_ & LOAD_PREFERRING_CACHE) ||
         partial_.get()) {
+      if (effective_load_flags_ & LOAD_PREFERRING_CACHE)
+        infinite_cache_transaction_->OnBackForwardNavigation();

[gavinp, 2012/10/26 22:06:14]

Oops: I made this comment on an earlier version but somehow it didn't get
uploaded. Have you considered reporting an enumeration giving which of these
flags was set, plus an extra bonus "NONE" field?

This is just a take it or leave it suggestion.

[rvargas (doing something else), 2012/10/26 22:36:12]

Kind of. I considered passing effective_load_flags_ to the simulation and having
histograms for other stuff, but I decided it was better not to do that.

This is at a layer that is not exactly what concerns the simulation (and the
same thing can be said about sending back navigations, but we want to be able to
compare that number with the people on the experiment).

What I mean is that the purpose of the simulation is to measure the behavior of
a very big cache, and the percentage of request issued with a particular flag
doesn't have anything to do with having a big cache or not, so if we really care
about that we could just as well add a regular histogram somewhere else.

       infinite_cache_transaction_.reset();
     } else {
       infinite_cache_transaction_->OnRequestStart(request);
     }
   }
 
   // We have to wait until the backend is initialized so we start the SM.
   next_state_ = STATE_GET_BACKEND;
   int rv = DoLoop(OK);
 
@@ skipping 2207 matching lines @@
 }
 
 int HttpCache::Transaction::ResetCacheIOStart(int return_value) {
   DCHECK(cache_io_start_.is_null());
   if (return_value == ERR_IO_PENDING)
     cache_io_start_ = base::TimeTicks::Now();
   return return_value;
 }
 
 }  // namespace net