Replace HistoryQuickProvider protobuf-based caching with an SQLite-based database.

sql/diagnostic_error_delegate.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.
 
 #ifndef SQL_DIAGNOSTIC_ERROR_DELEGATE_H_
 #define SQL_DIAGNOSTIC_ERROR_DELEGATE_H_
 
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "sql/connection.h"
 #include "sql/sql_export.h"
 
 namespace sql {
 
+// The histogram values from sqlite result codes currently range from 1 to 26
+// but 50 gives them room to grow.
+static const int kMaxSqliteError = 50;
+
 // This class handles the exceptional sqlite errors that we might encounter
 // if for example the db is corrupted. Right now we just generate a UMA
 // histogram for release and an assert for debug builds.
 //
 // Why is it a template you ask? well, that is a funny story. The histograms
 // need to be singletons that is why they are always static at the function
 // scope, but we cannot use the Singleton class because they are not default
 // constructible. The template parameter makes the compiler to create unique
 // classes that don't share the same static variable.
 template <class UniqueT>
 class DiagnosticErrorDelegate : public ErrorDelegate {
  public:
 
   virtual int OnError(int error, Connection* connection,
                       Statement* stmt) {
     LOG(ERROR) << "sqlite error " << error
                << ", errno " << connection->GetLastErrno()
                << ": " << connection->GetErrorMessage();
     RecordErrorInHistogram(error);
     return error;
   }
 
  private:
   static void RecordErrorInHistogram(int error) {
     // Trim off the extended error codes.
     error &= 0xff;
 
-    // The histogram values from sqlite result codes go currently from 1 to
-    // 26 currently but 50 gives them room to grow.
-    UMA_HISTOGRAM_ENUMERATION(UniqueT::name(), error, 50);
+    UMA_HISTOGRAM_ENUMERATION(UniqueT::name(), error, kMaxSqliteError);
   }
 };
 
 }  // namespace sql
 
 #endif  // SQL_DIAGNOSTIC_ERROR_DELEGATE_H_