Use a Finch Experiment to control the Browser Blacklist

chrome/browser/chrome_elf_init_win.cc

+// Copyright 2014 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/metrics/field_trial.h"
+#include "base/metrics/histogram.h"
+#include "base/strings/utf_string_conversions.h"
+#include "base/win/registry.h"
+#include "chrome/browser/chrome_elf_init_win.h"
+#include "chrome/common/chrome_version_info.h"
+#include "chrome_elf/blacklist/blacklist.h"
+
+namespace {
+
+const char kBrowserBlacklistTrialName[] = "BrowserBlacklist";
+const char kBrowserBlacklistTrialEnabledGroupName[] = "Enabled";
+
+// This enum is used to define the buckets for an enumerated UMA histogram.
+// Hence,
+//   (a) existing enumerated constants should never be deleted or reordered, and
+//   (b) new constants should only be appended in front of
+//       BLACKLIST_SETUP_EVENT_MAX.
+enum BlacklistSetupEventType {
+  // The blacklist beacon has placed to enable the browser blacklisting.
+  BLACKLIST_SETUP_ENABLED = 0,
+
+  // The blacklist was successfully enabled.
+  BLACKLIST_SETUP_RAN_SUCCESSFULLY,
+
+  // The blacklist setup code failed to execute.
+  BLACKLIST_SETUP_FAILED,
+
+  // Always keep this at the end.
+  BLACKLIST_SETUP_EVENT_MAX,
+};
+
+void RecordBlacklistSetupEvent(BlacklistSetupEventType blacklist_setup_event) {
+  UMA_HISTOGRAM_ENUMERATION("Blacklist.Setup",
+                            blacklist_setup_event,
+                            BLACKLIST_SETUP_EVENT_MAX);
+}
+
+}  // namespace
+
+void InitializeChromeElf() {
+  if (base::FieldTrialList::FindFullName(kBrowserBlacklistTrialName) ==
+      kBrowserBlacklistTrialEnabledGroupName) {
+    BrowserBlacklistBeaconSetup();
+  } else {
+    // Disable the blacklist for all future runs by removing the beacon.
+    base::win::RegKey blacklist_registry_key(HKEY_CURRENT_USER);
+    blacklist_registry_key.DeleteKey(blacklist::kRegistryBeaconPath);
+  }
+}
+
+void BrowserBlacklistBeaconSetup() {
+  base::win::RegKey blacklist_registry_key(HKEY_CURRENT_USER,
+                                           blacklist::kRegistryBeaconPath,
+                                           KEY_QUERY_VALUE | KEY_SET_VALUE);
+
+  // Find the last recorded blacklist version and the current version.
+  base::string16 blacklist_version;
+  blacklist_registry_key.ReadValue(blacklist::kBeaconVersion,

[sky, 2014/01/07 23:15:08]

What will the effects be of someone running two versions of chrome with
different beacon versions (say a dev channel and stable channel with different
profile dirs)? Seems like the values will bounce around and that there may be
race conditions.

[csharp, 2014/01/08 21:07:07]

Different user installs should interact with each other since these values are
nested in HKEY_CURRENT_KEY. However, we could run into trouble with users that
canary and another channels installed.

I've fixed this issue by adding a check in the code that actually checks if it
is enabled or disabled to only be enabled if the proper beacon is set and the
version match. The collisions that occur just mean that the blacklist might be
disabled for some runs for no good reason, but a working version of chrome's
blacklist won't ever enable the blacklist for a broken version.

+                                   &blacklist_version);
+
+  chrome::VersionInfo version_info;
+  base::string16 current_version(base::UTF8ToUTF16(version_info.Version()));
+  if (blacklist_version != current_version) {
+    // The blacklist hasn't run for this version yet, so enable it.
+    LONG set_version = blacklist_registry_key.WriteValue(
+        blacklist::kBeaconVersion,
+        current_version.c_str());
+
+    LONG set_state = blacklist_registry_key.WriteValue(
+        blacklist::kBeaconState,
+        blacklist::BLACKLIST_ENABLED);
+
+    // Only report the blacklist as getting setup when both registry writes
+    // succeed, since otherwise the blacklist wasn't properly setup.
+    if (set_version == ERROR_SUCCESS && set_state == ERROR_SUCCESS) {

[sky, 2014/01/07 23:15:08]

nit: no {}

[csharp, 2014/01/08 21:07:07]

Done.

+      RecordBlacklistSetupEvent(BLACKLIST_SETUP_ENABLED);
+    }
+
+    // Don't try to record if the blacklist setup succeeded or failed in the
+    // run since it could have been from either this version or the previous
+    // version (since crashes occur before we set the version in the registry).
+  } else {
+    // The blacklist version didn't change, so record the results of the
+    // latest setup.
+    DWORD blacklist_state = blacklist::BLACKLIST_STATE_MAX;
+    blacklist_registry_key.ReadValueDW(blacklist::kBeaconState,
+                                       &blacklist_state);
+
+    // Record the results of the latest blacklist setup.
+    if (blacklist_state == blacklist::BLACKLIST_ENABLED) {
+      RecordBlacklistSetupEvent(BLACKLIST_SETUP_RAN_SUCCESSFULLY);
+    } else if (blacklist_state == blacklist::BLACKLIST_SETUP_RUNNING) {
+      RecordBlacklistSetupEvent(BLACKLIST_SETUP_FAILED);
+
+      // Since the setup failed, mark the blacklist as disabled so we don't
+      // try it again for this version.
+      blacklist_registry_key.WriteValue(blacklist::kBeaconState,
+                                        blacklist::BLACKLIST_DISABLED);
+    }
+  }
+}