sql: Make Connection::StatementRef use 1-based ref-counting.

0-based ref-counting is deprecated. 1-based counting is described in
//base/memory/ref_counted.h. In summary, instaces must be created by
base::MakeRefCounted<T> or (less ideal) base::AdoptRef(new T).

This CL switches Connection::StatementRef to 1-based ref-counting, and

std::move()'s scoped_refptr<StatementRef> in a few places where that
avoids refcount churn.

Bug: none
Change-Id: I14755dc2482f18c8a9582066104f346c2873941d
Reviewed-on: https://chromium-review.googlesource.com/1137848
Commit-Queue: Victor Costan <pwnall@chromium.org>
Reviewed-by: Chris Mumford <cmumford@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575876}

sql/connection.cc

@@ -1435,7 +1435,7 @@ scoped_refptr<Connection::StatementRef> Connection::GetStatementImpl(
 
   // Return inactive statement.
   if (!db_)
-    return new StatementRef(NULL, NULL, poisoned_);
+    return base::MakeRefCounted<StatementRef>(nullptr, nullptr, poisoned_);
 
   sqlite3_stmt* stmt = NULL;
   int rc = sqlite3_prepare_v2(db_, sql, -1, &stmt, NULL);
@@ -1445,9 +1445,9 @@ scoped_refptr<Connection::StatementRef> Connection::GetStatementImpl(
 
     // It could also be database corruption.
     OnSqliteError(rc, NULL, sql);
-    return new StatementRef(NULL, NULL, false);
+    return base::MakeRefCounted<StatementRef>(nullptr, nullptr, false);
   }
-  return new StatementRef(tracking_db, stmt, true);
+  return base::MakeRefCounted<StatementRef>(tracking_db, stmt, true);
 }
 
 scoped_refptr<Connection::StatementRef> Connection::GetUntrackedStatement(

sql/connection.h

@@ -581,6 +581,8 @@ class SQL_EXPORT Connection {
   // should always check validity before using.
   class SQL_EXPORT StatementRef : public base::RefCounted<StatementRef> {
    public:
+    REQUIRE_ADOPTION_FOR_REFCOUNTED_TYPE();
+
     // |connection| is the sql::Connection instance associated with
     // the statement, and is used for tracking outstanding statements
     // and for error handling.  Set to NULL for invalid or untracked

sql/statement.cc

@@ -18,16 +18,14 @@ namespace sql {
 // we don't have to NULL-check the ref_ to see if the statement is valid: we
 // only have to check the ref's validity bit.
 Statement::Statement()
-    : ref_(new Connection::StatementRef(NULL, NULL, false)),
+    : ref_(base::MakeRefCounted<Connection::StatementRef>(nullptr,
+                                                          nullptr,
+                                                          false)),
       stepped_(false),
-      succeeded_(false) {
-}
+      succeeded_(false) {}
 
 Statement::Statement(scoped_refptr<Connection::StatementRef> ref)
-    : ref_(ref),
-      stepped_(false),
-      succeeded_(false) {
-}
+    : ref_(std::move(ref)), stepped_(false), succeeded_(false) {}
 
 Statement::~Statement() {
   // Free the resources associated with this statement. We assume there's only
@@ -38,11 +36,12 @@ Statement::~Statement() {
 
 void Statement::Assign(scoped_refptr<Connection::StatementRef> ref) {
   Reset(true);
-  ref_ = ref;
+  ref_ = std::move(ref);
 }
 
 void Statement::Clear() {
-  Assign(new Connection::StatementRef(NULL, NULL, false));
+  Assign(
+      base::MakeRefCounted<Connection::StatementRef>(nullptr, nullptr, false));
   succeeded_ = false;
 }