Adding DiskBasedCertCache to HttpCache (+UMA).

net/http/disk_based_cert_cache.cc

Index: net/http/disk_based_cert_cache.cc
diff --git a/net/http/disk_based_cert_cache.cc b/net/http/disk_based_cert_cache.cc
index b6c5b7e2731b5ede6215fefe0f2ffceba679f5e6..62e77aae15ada0841ffeb14abfd679826565af09 100644
--- a/net/http/disk_based_cert_cache.cc
+++ b/net/http/disk_based_cert_cache.cc
@@ -9,6 +9,7 @@
 #include "base/bind.h"
 #include "base/callback_helpers.h"
 #include "base/memory/ref_counted.h"
+#include "base/metrics/histogram.h"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "net/base/io_buffer.h"
@@ -19,9 +20,17 @@ namespace net {
 
 namespace {
 
+// TODO(brandonsalmon): remove when more data no longer needed.
+void RecordHistogram(int rv) {
+  bool already_existed = (rv < 0);
+  UMA_HISTOGRAM_BOOLEAN(
+      "DiskBasedCertCache.WritePreviouslyExisted", already_existed);

[Ryan Sleevi, 2014/06/26 19:56:02]

You will need to update histograms.xml to ad this

[brandonsalmon, 2014/06/26 22:04:42]

What do I need to do to update this? I tried and git started acting weird.

+}
+
 // Used to obtain a unique cache key for a certificate in the form of
 // "cert:<hash>".
-std::string GetCacheKeyToCert(const X509Certificate::OSCertHandle cert_handle) {
+std::string GetCacheKeyToCert(
+       const X509Certificate::OSCertHandle cert_handle) {

[Ryan Sleevi, 2014/06/26 19:56:02]

Seems like this fit before - why the change?

   SHA1HashValue fingerprint =
       X509Certificate::CalculateFingerprint(cert_handle);
 
@@ -29,7 +38,7 @@ std::string GetCacheKeyToCert(const X509Certificate::OSCertHandle cert_handle) {
          base::HexEncode(fingerprint.data, arraysize(fingerprint.data));
 }
 
-}  // namespace
+} // namespace

[Ryan Sleevi, 2014/06/26 19:56:02]

This was correct the way it was before (two spaces before // )

 
 // WriteWorkers represent pending Set jobs in the DiskBasedCertCache. Each
 // certificate requested to be cached is assigned a Writeworker on a one-to-one
@@ -191,6 +200,7 @@ int DiskBasedCertCache::WriteWorker::DoCreateComplete(int rv) {
   // An error here usually signifies that the entry already exists.
   // If this occurs, it is necessary to instead open the previously
   // existing entry.
+  RecordHistogram(rv);

[Ryan Sleevi, 2014/06/26 19:56:02]

Sanity check: What would you expect to use this information for? How would it
influence the design?

[brandonsalmon, 2014/06/26 22:04:42]

I added this because it seemed important to gather data on how often a
certificate is overwritten on disk (it was my assumption that this would
correspond to duplicate writes in the currently used method).

   if (rv < 0) {
     state_ = STATE_OPEN;
     return OK;