Add fxcrt::AutoRestorer<T>::AbandonRestoration().chromium/3475

Kinda like reaching a commit point, makes going forward more useful.

Change-Id: I7695b6e627d4cd8ed2bccb667d0cabd7f42c7b1c
Reviewed-on: https://pdfium-review.googlesource.com/35970
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

2 files changed, 29 insertions, 2 deletions

diff --git a/core/fxcrt/autorestorer.h b/core/fxcrt/autorestorer.h
index 745a56fff2..cafa075137 100644
--- a/core/fxcrt/autorestorer.h
+++ b/core/fxcrt/autorestorer.h
@@ -12,10 +12,14 @@ class AutoRestorer {
  public:
   explicit AutoRestorer(T* location)
       : m_Location(location), m_OldValue(*location) {}
-  ~AutoRestorer() { *m_Location = m_OldValue; }
+  ~AutoRestorer() {
+    if (m_Location)
+      *m_Location = m_OldValue;
+  }
+  void AbandonRestoration() { m_Location = nullptr; }
 
  private:
-  T* const m_Location;
+  T* m_Location;
   const T m_OldValue;
 };
 
diff --git a/core/fxcrt/autorestorer_unittest.cpp b/core/fxcrt/autorestorer_unittest.cpp
new file mode 100644
index 0000000000..ac1d613e7c
--- /dev/null
+++ b/core/fxcrt/autorestorer_unittest.cpp
@@ -0,0 +1,23 @@
+// Copyright 2018 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "core/fxcrt/autorestorer.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+TEST(fxcrt, AutoRestorer) {
+  int x = 5;
+  {
+    AutoRestorer<int> restorer(&x);
+    x = 6;
+    EXPECT_EQ(6, x);
+  }
+  EXPECT_EQ(5, x);
+  {
+    AutoRestorer<int> restorer(&x);
+    x = 6;
+    EXPECT_EQ(6, x);
+    restorer.AbandonRestoration();
+  }
+  EXPECT_EQ(6, x);
+}