Add UMA statistics for tracking session storage database opening failures.

webkit/dom_storage/session_storage_database.cc

Index: webkit/dom_storage/session_storage_database.cc
diff --git a/webkit/dom_storage/session_storage_database.cc b/webkit/dom_storage/session_storage_database.cc
index b22ea30296bd01e45593eb5e10f440c027ead4f8..ba4c021768504d170f6e12ab83edbe930762cded 100644
--- a/webkit/dom_storage/session_storage_database.cc
+++ b/webkit/dom_storage/session_storage_database.cc
@@ -6,6 +6,7 @@
 
 #include "base/file_util.h"
 #include "base/logging.h"
+#include "base/metrics/histogram.h"
 #include "base/stringprintf.h"
 #include "base/string_number_conversions.h"
 #include "base/utf_string_conversions.h"
@@ -16,6 +17,17 @@
 #include "third_party/leveldatabase/src/include/leveldb/options.h"
 #include "third_party/leveldatabase/src/include/leveldb/write_batch.h"
 
+namespace {
+

[michaeln, 2013/02/27 00:31:57]

Can you define a constant for histogram name value here too.

[marja, 2013/02/27 08:48:25]

Done. I just #define'd it, because we cannot have a std::string here, that would
create a non-trivial static initializer afaics... const char* would work, but it
seems to be discouraged. Let me know if you'd like something else than a
#define.

[michaeln, 2013/02/27 20:31:48]

I would expect compilers to optimize the multiple uses into one byte sequence in
the binary but its a leap of faith. Elsewhere we do like this...
const char kHttpScheme[] = "http";

+enum SessionStorageUMA {
+  SESSION_STORAGE_UMA_SUCCESS,
+  SESSION_STORAGE_UMA_RECREATED,
+  SESSION_STORAGE_UMA_FAIL,
+  SESSION_STORAGE_UMA_MAX
+};
+
+}  // namespace
+
 // Layout of the database:
 // | key                            | value                              |
 // -----------------------------------------------------------------------
@@ -286,10 +298,20 @@ bool SessionStorageDatabase::LazyOpen(bool create_if_needed) {
     if (!s.ok()) {
       LOG(WARNING) << "Failed to open leveldb in " << file_path_.value()
                    << ", error: " << s.ToString();
+      UMA_HISTOGRAM_ENUMERATION("SessionStorageDatabase.Open",
+                                SESSION_STORAGE_UMA_FAIL,
+                                SESSION_STORAGE_UMA_MAX);
       DCHECK(db == NULL);
       db_error_ = true;
       return false;
     }
+    UMA_HISTOGRAM_ENUMERATION("SessionStorageDatabase.Open",
+                              SESSION_STORAGE_UMA_RECREATED,
+                              SESSION_STORAGE_UMA_MAX);
+  } else {
+    UMA_HISTOGRAM_ENUMERATION("SessionStorageDatabase.Open",
+                              SESSION_STORAGE_UMA_SUCCESS,
+                              SESSION_STORAGE_UMA_MAX);
   }
   db_.reset(db);
   return true;