Move ErrorDelegate to its own file and add static utility functions to ErrorDelegate

sql/diagnostic_error_delegate.h

Index: sql/diagnostic_error_delegate.h
diff --git a/sql/diagnostic_error_delegate.h b/sql/diagnostic_error_delegate.h
index 4b8ce323018a158e6b42ed6eebedaeb78d7b18a4..78b3d9d8155217adbec54abb9e135d080c95d684 100644
--- a/sql/diagnostic_error_delegate.h
+++ b/sql/diagnostic_error_delegate.h
@@ -6,8 +6,8 @@
 #define SQL_DIAGNOSTIC_ERROR_DELEGATE_H_
 
 #include "base/logging.h"
-#include "base/metrics/histogram.h"
 #include "sql/connection.h"
+#include "sql/error_delegate_util.h"
 #include "sql/sql_export.h"
 
 namespace sql {
@@ -15,12 +15,8 @@ namespace sql {
 // 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.
+// See error_delegate_util.h for an explanation as to why this class is a
+// template.
 template <class UniqueT>
 class DiagnosticErrorDelegate : public ErrorDelegate {
  public:
@@ -29,24 +25,12 @@ class DiagnosticErrorDelegate : public ErrorDelegate {
 
   virtual int OnError(int error, Connection* connection,
                       Statement* stmt) {
-    LOG(ERROR) << "sqlite error " << error
-               << ", errno " << connection->GetLastErrno()
-               << ": " << connection->GetErrorMessage();
-    RecordErrorInHistogram(error);
+    LogAndRecordErrorInHistogram<UniqueT>(error, connection);
     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);
-  }
-
- DISALLOW_COPY_AND_ASSIGN(DiagnosticErrorDelegate);
+  DISALLOW_COPY_AND_ASSIGN(DiagnosticErrorDelegate);
 };
 
 }  // namespace sql