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

base/test/mock_entropy_provider.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 "base/test/mock_entropy_provider.h"
 
 namespace base {
 
+MockEntropyProvider::MockEntropyProvider() : entropy_value_(0.5) {}
+MockEntropyProvider::MockEntropyProvider(double entropy_value)
+    : entropy_value_(entropy_value) {}
 MockEntropyProvider::~MockEntropyProvider() {}
 
 double MockEntropyProvider::GetEntropyForTrial(
     const std::string& trial_name,
     uint32_t randomization_seed) const {
-  return 0.5;
+  return entropy_value_;
 }
 
 }  // namespace base