[HttpCache] Measure causes for cache validation requests

net/http/http_cache_transaction.h

 // 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.
 
 // This file declares HttpCache::Transaction, a private class of HttpCache so
 // it should only be included by http_cache.cc
 
 #ifndef NET_HTTP_HTTP_CACHE_TRANSACTION_H_
 #define NET_HTTP_HTTP_CACHE_TRANSACTION_H_
 
@@ skipping 228 matching lines @@
     PATTERN_UNDEFINED,
     PATTERN_NOT_COVERED,
     PATTERN_ENTRY_NOT_CACHED,
     PATTERN_ENTRY_USED,
     PATTERN_ENTRY_VALIDATED,
     PATTERN_ENTRY_UPDATED,
     PATTERN_ENTRY_CANT_CONDITIONALIZE,
     PATTERN_MAX,
   };
 
+  // Used for categorizing validation triggers in histograms.
+  // NOTE: This enumeration is used in histograms, so please do not add entries
+  // in the middle.
+  enum ValidationCause {

[gavinp, 2016/05/12 15:02:02]

Could we use an enum class here?

[jkarlin, 2016/05/13 15:06:51]

We could, but we'd still have to static_cast the histogram calls. 

+    VALIDATION_CAUSE_UNDEFINED,
+    VALIDATION_CAUSE_VARY_MISMATCH,
+    VALIDATION_CAUSE_VALIDATE_FLAG,
+    VALIDATION_CAUSE_STALE,
+    VALIDATION_CAUSE_ZERO_FRESHNESS,
+    VALIDATION_CAUSE_MAX
+  };
+
   // Runs the state transition loop. Resets and calls |callback_| on exit,
   // unless the return value is ERR_IO_PENDING.
   int DoLoop(int result);
 
   // Each of these methods corresponds to a State value.  If there is an
   // argument, the value corresponds to the return of the previous state or
   // corresponding callback.
   int DoGetBackend();
   int DoGetBackendComplete(int result);
   int DoInitEntry();
@@ skipping 202 matching lines @@
   int io_buf_len_;
   int read_offset_;
   int effective_load_flags_;
   int write_len_;
   std::unique_ptr<PartialData> partial_;  // We are dealing with range requests.
   UploadProgress final_upload_progress_;
   CompletionCallback io_callback_;
 
   // Members used to track data for histograms.
   TransactionPattern transaction_pattern_;
+  ValidationCause validation_cause_;
   base::TimeTicks entry_lock_waiting_since_;
   base::TimeTicks first_cache_access_since_;
   base::TimeTicks send_request_since_;
 
   int64_t total_received_bytes_;
   int64_t total_sent_bytes_;
 
   // Load timing information for the last network request, if any.  Set in the
   // 304 and 206 response cases, as the network transaction may be destroyed
   // before the caller requests load timing information.
@@ skipping 13 matching lines @@
   BeforeProxyHeadersSentCallback before_proxy_headers_sent_callback_;
 
   base::WeakPtrFactory<Transaction> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(Transaction);
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_CACHE_TRANSACTION_H_