Add StaleWhileRevalidateExperiment histograms.

net/base/stale_while_revalidate_experiment_domains.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 "net/base/stale_while_revalidate_experiment_domains.h"
+
+#include <stddef.h>
+
+#include "base/logging.h"
+#include "net/base/lookup_string_in_fixed_set.h"
+
+namespace net {
+
+namespace {
+
+#include "net/base/stale_while_revalidate_experiment_domains-inc.cc"
+
+// The maximum number of dots in any domain in the list. This is used to ignore
+// parts of the host name that are irrelevant, and so must be correct.
+const int kMaxDots = 2;
+
+// The minimum number of dots in a host necessary for it to be considered a
+// match.
+const int kMinDots = 1;
+
+const size_t npos = base::StringPiece::npos;
+
+bool LookupTail(const base::StringPiece& host, size_t pos) {
+  DCHECK_LT(pos, host.size());
+  return LookupStringInFixedSet(kDafsa, sizeof(kDafsa), host.data() + pos,
+                                host.size() - pos) == 0;
+}
+
+bool LookupTrimmedHost(const base::StringPiece& trimmed) {
+  // |trimmed| contains at least one non-dot. The maximum number of dots we want
+  // to look for is kMaxInterestingDots; any dots before that will not affect
+  // the outcome of the match.
+  const int kMaxInterestingDots = kMaxDots + 1;
+
+  // Scan |trimmed| from the right for up to kMaxInterestingDots dots, checking
+  // for a domain match at each position.
+  int found_dots = 0;
+  size_t pos = npos;
+  while (found_dots < kMaxInterestingDots) {
+    pos = trimmed.find_last_of('.', pos);
+    if (pos == npos)
+      break;
+    ++found_dots;
+    if (found_dots > kMinDots && LookupTail(trimmed, pos + 1))
+      return true;
+    if (pos == 0)
+      return false;
+    --pos;
+  }
+
+  if (found_dots >= kMinDots && found_dots <= kMaxDots) {
+    // We might have an exact match.
+    return LookupTail(trimmed, 0);
+  }
+
+  return false;
+}
+
+}  // namespace
+
+bool IsHostInStaleWhileRevalidateExperimentDomain(
+    const base::StringPiece& host) {
+  // Ignore trailing dots.
+  size_t last_interesting_pos = host.find_last_not_of('.');
+  if (last_interesting_pos == npos)
+    return false;
+
+  return LookupTrimmedHost(host.substr(0, last_interesting_pos + 1));
+}
+
+}  // namespace net