Simulate field trial assignments with new variations seed.

components/variations/variations_seed_simulator.h

Index: components/variations/variations_seed_simulator.h
===================================================================
--- components/variations/variations_seed_simulator.h	(revision 0)
+++ components/variations/variations_seed_simulator.h	(working copy)
@@ -0,0 +1,56 @@
+// Copyright 2013 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 COMPONENTS_VARIATIONS_VARIATIONS_SEED_SIMULATOR_H_
+#define COMPONENTS_VARIATIONS_VARIATIONS_SEED_SIMULATOR_H_
+
+#include <string>
+#include <vector>
+
+#include "base/compiler_specific.h"
+#include "base/gtest_prod_util.h"
+#include "base/metrics/field_trial.h"
+
+namespace chrome_variations {
+
+class ProcessedStudy;
+
+// VariationsSeedSimulator simulates the result of creating a set of studies
+// and detecting which studies would result in group changes.
+class VariationsSeedSimulator {
+ public:
+  // Creates the simulator with the given entropy |provider|.
+  explicit VariationsSeedSimulator(
+      const base::FieldTrial::EntropyProvider& provider);
+  virtual ~VariationsSeedSimulator();
+
+  // Computes differences between the current process' field trial state and
+  // the result of evaluating the |processed_studies| list. It is expected that
+  // |processed_studies| have already been filtered and only contain studies
+  // that apply to the configuration being simulated. Returns the number of
+  // studies that are expected to change groups.

[jwd, 2014/01/07 18:31:37]

small nit: Wording seems a bit imprecise. It's actually giving a lower bound on
the changed groups, due to the session randomized portion.

[Alexei Svitkine (slow), 2014/01/08 15:17:35]

Done.

+  int ComputeDifferences(
+      const std::vector<ProcessedStudy>& processed_studies);
+
+ private:
+  // For the given |processed_study| with PERMANENT consistency, simulates group
+  // assignment and returns true if the result differs from that study's group
+  // in the current process.
+  bool PermanentStudyGroupChanged(const ProcessedStudy& processed_study,
+                                  const std::string& selected_group);
+
+  // For the given |processed_study| with SESSION consistency, determines if
+  // there are enough changes in the study config that restarting will result
+  // in a guaranteed different group assignment (or different params).
+  bool SessionStudyGroupChanged(const ProcessedStudy& filtered_study,
+                                const std::string& selected_group);
+
+  const base::FieldTrial::EntropyProvider& entropy_provider_;
+
+  DISALLOW_COPY_AND_ASSIGN(VariationsSeedSimulator);
+};
+
+}  // namespace chrome_variations
+
+#endif  // COMPONENTS_VARIATIONS_VARIATIONS_SEED_SIMULATOR_H_