Add HttpCache.ExternallyConditionalized histogram.

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 220 matching lines @@
 
 void RecordNoStoreHeaderHistogram(int load_flags,
                                   const net::HttpResponseInfo* response) {
   if (load_flags & net::LOAD_MAIN_FRAME) {
     UMA_HISTOGRAM_BOOLEAN(
         "Net.MainFrameNoStore",
         response->headers->HasHeaderValue("cache-control", "no-store"));
   }
 }
 
+enum ExternallyConditionalizedType {
+  EXTERNALLY_CONDITIONALIZED_CACHE_REQUIRES_VALIDATION,
+  EXTERNALLY_CONDITIONALIZED_CACHE_USABLE,
+  EXTERNALLY_CONDITIONALIZED_MISMATCHED_VALIDATORS,
+  EXTERNALLY_CONDITIONALIZED_MAX
+};
+
 }  // namespace
 
 namespace net {
 
 struct HeaderNameAndValue {
   const char* name;
   const char* value;
 };
 
 // If the request includes one of these request headers, then avoid caching
@@ skipping 1968 matching lines @@
 
     if (response_.headers->response_code() != 200 || truncated_ ||
         validator.empty() || validator != external_validation_.values[i]) {
       // The externally conditionalized request is not a validation request
       // for our existing cache entry. Proceed with caching disabled.
       UpdateTransactionPattern(PATTERN_NOT_COVERED);
       DoneWritingToEntry(true);
     }
   }
 
+  // TODO(ricea): This calculation is expensive to perform just to collect
+  // statistics. Either remove it or use the result, depending on the result of
+  // the experiment.
+  ExternallyConditionalizedType type =
+      EXTERNALLY_CONDITIONALIZED_CACHE_USABLE;
+  if (mode_ == NONE)
+    type = EXTERNALLY_CONDITIONALIZED_MISMATCHED_VALIDATORS;
+  else if (RequiresValidation())
+    type = EXTERNALLY_CONDITIONALIZED_CACHE_REQUIRES_VALIDATION;
+  // TODO(ricea): Add CACHE_USABLE_STALE once stale-while-revalidate CL landed.

[rvargas (doing something else), 2014/09/04 19:33:20]

tiny nit: Please add an empty line above this line.

[Adam Rice, 2014/09/05 05:49:29]

Done.

+  // TODO(ricea): Either remove this histogram or make it permanent by M40.
+  UMA_HISTOGRAM_ENUMERATION("HttpCache.ExternallyConditionalized",
+                            type,
+                            EXTERNALLY_CONDITIONALIZED_MAX);
+
   next_state_ = STATE_SEND_REQUEST;
   return OK;
 }
 
 int HttpCache::Transaction::RestartNetworkRequest() {
   DCHECK(mode_ & WRITE || mode_ == NONE);
   DCHECK(network_trans_.get());
   DCHECK_EQ(STATE_NONE, next_state_);
 
   next_state_ = STATE_SEND_REQUEST_COMPLETE;
@@ skipping 630 matching lines @@
     default:
       NOTREACHED();
   }
 }
 
 void HttpCache::Transaction::OnIOComplete(int result) {
   DoLoop(result);
 }
 
 }  // namespace net