Update from https://crrev.com/304121

base/files/file.h

Index: base/files/file.h
diff --git a/base/files/file.h b/base/files/file.h
index 4110d51bd8199bde0b1e0f4e79d8fa5c7ae9e51e..7b6366c1c2edaa2c6ccb695f2f075ff83f0d002b 100644
--- a/base/files/file.h
+++ b/base/files/file.h
@@ -19,6 +19,7 @@
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/files/scoped_file.h"
+#include "base/gtest_prod_util.h"
 #include "base/move.h"
 #include "base/time/time.h"
 
@@ -26,6 +27,8 @@
 #include "base/win/scoped_handle.h"
 #endif
 
+FORWARD_DECLARE_TEST(FileTest, MemoryCorruption);
+
 namespace base {
 
 class FilePath;
@@ -296,12 +299,59 @@ class BASE_EXPORT File {
   static std::string ErrorToString(Error error);
 
  private:
+  FRIEND_TEST_ALL_PREFIXES(::FileTest, MemoryCorruption);
+
+#if defined(OS_POSIX)
+  // Encloses a single ScopedFD, saving a cheap tamper resistent memory checksum
+  // alongside it. This checksum is validated at every access, allowing early
+  // detection of memory corruption.
+
+  // TODO(gavinp): This is in place temporarily to help us debug
+  // https://crbug.com/424562 , which can't be reproduced in valgrind. Remove
+  // this code after we have fixed this issue.
+  class MemoryCheckingScopedFD {
+   public:
+    MemoryCheckingScopedFD();
+    MemoryCheckingScopedFD(int fd);
+    ~MemoryCheckingScopedFD();
+
+    bool is_valid() const { Check(); return file_.is_valid(); }
+    int get() const { Check(); return file_.get(); }
+
+    void reset() { Check(); file_.reset(); UpdateChecksum(); }
+    void reset(int fd) { Check(); file_.reset(fd); UpdateChecksum(); }
+    int release() {
+      Check();
+      int fd = file_.release();
+      UpdateChecksum();
+      return fd;
+    }
+
+   private:
+    FRIEND_TEST_ALL_PREFIXES(::FileTest, MemoryCorruption);
+
+    // Computes the checksum for the current value of |file_|. Returns via an
+    // out parameter to guard against implicit conversions of unsigned integral
+    // types.
+    void ComputeMemoryChecksum(unsigned int* out_checksum) const;
+
+    // Confirms that the current |file_| and |file_memory_checksum_| agree,
+    // failing a CHECK if they do not.
+    void Check() const;
+
+    void UpdateChecksum();
+
+    ScopedFD file_;
+    unsigned int file_memory_checksum_;
+  };
+#endif
+
   void SetPlatformFile(PlatformFile file);
 
 #if defined(OS_WIN)
   win::ScopedHandle file_;
 #elif defined(OS_POSIX)
-  ScopedFD file_;
+  MemoryCheckingScopedFD file_;
 #endif
 
   Error error_details_;