Add sampling of unknown filetypes in download protection.

chrome/common/safe_browsing/file_type_policies_test_util.h

Index: chrome/common/safe_browsing/file_type_policies_test_util.h
diff --git a/chrome/common/safe_browsing/file_type_policies_test_util.h b/chrome/common/safe_browsing/file_type_policies_test_util.h
new file mode 100644
index 0000000000000000000000000000000000000000..f4f728001353463a6955ec3835d39b972c86560e
--- /dev/null
+++ b/chrome/common/safe_browsing/file_type_policies_test_util.h
@@ -0,0 +1,43 @@
+// Copyright 2016 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.
+
+#ifndef CHROME_COMMON_SAFE_BROWSING_FILE_TYPE_POLICIES_TEST_UTIL_H_
+#define CHROME_COMMON_SAFE_BROWSING_FILE_TYPE_POLICIES_TEST_UTIL_H_
+
+#include "chrome/common/safe_browsing/file_type_policies.h"
+
+namespace safe_browsing {
+
+// This is a test fixture for modifying the proto with FileTypePolicies.
+// While an object of this class is in scope, it will cause callers
+// of FileTypePolicies::GetInstance() to see the modified list.
+// When it goes out of scope, future callers will get the unmodified
+// global list.
+//
+// Example:
+//   FileTypePoliciesTestOverlay policies_overlay_;
+//   auto pb = policies_overlay_.GetConfig();  // DownloadFileTypes
+//   pb.set_sampled_ping_probability(1.0);
+//   policies_overlay_.SetConfig(pb)
+//   ...
+class FileTypePoliciesTestOverlay {
+ public:
+  FileTypePoliciesTestOverlay();
+  ~FileTypePoliciesTestOverlay();
+
+  DownloadFileTypeConfig GetConfig() const {
+    return policies_->GetConfigForTesting();
+  }
+
+  void SetConfig(const DownloadFileTypeConfig& new_config) {
+    policies_->SetConfigForTesting(new_config);

[asanka, 2016/06/20 18:15:46]

Can we have something like a SwapConfigForTesting that we can call directly on
the singleton? That way we won't need to rework how
FileTypePolicies::GetInstance() works. THat would allow
FileTypePoliciesTestOveraly to restore the state of the FileTypePolicies without
having to swap the instance out.

Or just a SwapConfig() method that can be used by PopulateFromBinaryPb as well
as FileTypePoliciesTestOverlay.

I'm suggesting this because FileTypePolicies should be updateable at runtime
anyway. It seems we aren't saving any logic by swapping out FileTypePolicies.

[Nathan Parker, 2016/06/20 22:47:31]

Sure, SGTM.  Done.

+  }
+
+ private:
+  std::unique_ptr<FileTypePolicies> policies_;
+};
+
+}  // namespace safe_browsing
+
+#endif  // CHROME_COMMON_SAFE_BROWSING_FILE_TYPE_POLICIES_TEST_UTIL_H_