Adding a new component, Previews.

components/previews/previews_experiments.cc

Index: components/previews/previews_experiments.cc
diff --git a/components/previews/previews_experiments.cc b/components/previews/previews_experiments.cc
new file mode 100644
index 0000000000000000000000000000000000000000..64ded70b3fc21272ccce42641668aef5f6ef018b
--- /dev/null
+++ b/components/previews/previews_experiments.cc
@@ -0,0 +1,47 @@
+// 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.
+
+#include "components/previews/previews_experiments.h"
+
+#include <map>
+#include <string>
+
+#include "base/metrics/field_trial.h"
+#include "base/strings/string_util.h"
+#include "components/variations/variations_associated_data.h"
+
+namespace {
+
+// The group of client side previews experiments.
+const char kClientSidePreviewsFieldTrial[] = "ClientSidePreviewsFieldTrial";

[bengr, 2016/07/26 23:54:21]

I would use the string "ClientSidePreviews" instead of
"ClientSidePreviewsFieldTrial"

[RyanSturm, 2016/07/27 16:27:48]

Done.

+
+const char kEnabled[] = "Enabled";
+
+// Allow offline pages to show for prohibitively slow networks.
+const char kOfflinePagesSlowNetwork[] = "show_offline_pages";
+
+}  // namespace
+
+namespace previews {
+
+bool IsIncludedInClientSidePreviewsExperimentsFieldTrial() {
+  return base::StartsWith(

[bengr, 2016/07/26 23:54:21]

Add a comment that says:
// By convention, an experiment in the client-side previews study enables use of
at least one client-side previews optimization if its name begins with
"Enabled."

[RyanSturm, 2016/07/27 16:27:48]

Done.

+      base::FieldTrialList::FindFullName(kClientSidePreviewsFieldTrial),
+      kEnabled, base::CompareCase::SENSITIVE);
+}
+
+bool IsIncludedInOfflinePagesSlowConnectionFieldTrial() {

[bengr, 2016/07/26 23:54:21]

Change the name to IsOfflinePreviewsEnabled()

[RyanSturm, 2016/07/27 16:27:48]

Done.

+  if (!IsIncludedInClientSidePreviewsExperimentsFieldTrial())
+    return false;
+  std::map<std::string, std::string> client_side_params;

[bengr, 2016/07/26 23:54:21]

client_side_params -> experiment_params

[RyanSturm, 2016/07/27 16:27:48]

Done.

+  if (!variations::GetVariationParams(kClientSidePreviewsFieldTrial,
+                                      &client_side_params)) {
+    return false;
+  }
+  std::map<std::string, std::string>::const_iterator it =
+      client_side_params.find(kOfflinePagesSlowNetwork);
+  return it != client_side_params.end() && it->second == "true";
+}
+
+}  // namespace previews