Fix sandbox ASan test to cope with forward slashes in __FILE__

sandbox/win/src/address_sanitizer_test.cc

 // Copyright 2015 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.
 
 #include <stdio.h>
 
 #include "base/environment.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/files/scoped_temp_dir.h"
@@ skipping 75 matching lines @@
     EXPECT_EQ(123, result);
 
     std::string data;
     ASSERT_TRUE(base::ReadFileToString(base::FilePath(temp_file_name), &data));
     // Redirection uses a feature that was added in Windows Vista.
     ASSERT_TRUE(
         strstr(data.c_str(), "ERROR: AddressSanitizer: heap-buffer-overflow"))
         << "There doesn't seem to be an ASan report:\n" << data;
     ASSERT_TRUE(strstr(data.c_str(), "AddressSanitizerTests_Report"))
         << "The ASan report doesn't appear to be symbolized:\n" << data;
-    ASSERT_TRUE(strstr(data.c_str(), strrchr(__FILE__, '\\')))
+    std::string source_file_basename(__FILE__);
+    size_t last_slash = source_file_basename.find_last_of("/\\");
+    last_slash = last_slash == std::string::npos ? 0 : last_slash + 1;
+    ASSERT_TRUE(strstr(data.c_str(), &source_file_basename[last_slash]))
         << "The stack trace doesn't have a correct filename:\n" << data;
   } else {
     LOG(WARNING) << "Not an AddressSanitizer build, skipping the run.";
   }
 }
 
 }