Use low entropy for studies that send experiment IDs to Google properties.

base/test/mock_entropy_provider.h

 // 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.
 
 #ifndef BASE_TEST_MOCK_ENTROPY_PROVIDER_H_
 #define BASE_TEST_MOCK_ENTROPY_PROVIDER_H_
 
 #include <stdint.h>
 
 #include "base/metrics/field_trial.h"
 
 namespace base {
 
 class MockEntropyProvider : public base::FieldTrial::EntropyProvider {
  public:
+  MockEntropyProvider();
+  MockEntropyProvider(double entropy_value);

[Alexei Svitkine (slow), 2016/05/18 18:33:29]

Nit: explicit

   ~MockEntropyProvider() override;
 
   // base::FieldTrial::EntropyProvider:
   double GetEntropyForTrial(const std::string& trial_name,
                             uint32_t randomization_seed) const override;
+
+ private:
+  double entropy_value_;
+
+  DISALLOW_COPY_AND_ASSIGN(MockEntropyProvider);
 };
 
 }  // namespace base
 
 #endif  // BASE_TEST_MOCK_ENTROPY_PROVIDER_H_