Add a field trial for using lower sqlite cache sizes.

chrome/browser/history/history_field_trial.cc

+// Copyright (c) 2011 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 "chrome/browser/history/history_field_trial.h"
+
+#include "base/metrics/field_trial.h"
+
+namespace history {
+
+namespace {
+
+int g_low_mem_trial_group = 0;
+bool g_low_mem_trial = false;
+
+static const char kHistoryFieldTrialName[] = "History";
+
+}  // namespace
+
+// static
+void HistoryFieldTrial::Activate() {
+  if (g_low_mem_trial_group)
+    return;  // Already initialized.
+
+  scoped_refptr<base::FieldTrial> trial(new base::FieldTrial(
+      kHistoryFieldTrialName, 1000, "Inactive", 2012, 2, 1));
+
+  // Try to give the user a consistent experience, if possible.

[jar (doing other things), 2011/10/24 18:40:55]

Why do we want "consistent" experience?  Are you expecting the  change to be
that dramatic?
Note that we get "better" data (better randomization, and hence lower variance I
think) if each use is allowed to randomly be in/out of the experiment with each
process launch (unless we allow users to self-select out, by restarting, or
such).

[Scott Hess - ex-Googler, 2011/10/24 19:15:27]

I would rather have a poor experience some of the time than a poor experience
every time, myself.

[brettw, 2011/10/25 01:55:02]

I actually wasn't entirely sure if this was good or bad, I just copied it from
other field trials. I removed it.

+  if (base::FieldTrialList::IsOneTimeRandomizationEnabled())
+    trial->UseOneTimeRandomization();
+
+  g_low_mem_trial_group = trial->AppendGroup("LowMem", 50);  // 5%
+  if (trial->group() == g_low_mem_trial_group)
+    g_low_mem_trial = true;
+}
+
+// static
+bool HistoryFieldTrial::IsLowMemFieldTrial() {
+  return g_low_mem_trial;
+}
+
+// static
+std::string HistoryFieldTrial::GetGroupSuffix() {
+  return g_low_mem_trial ? std::string("_LowMem") : std::string();
+}
+
+}  // namespace history