Add experiments info to crash dumps.

chrome/app/breakpad_field_trial_win.cc

+// Copyright (c) 2012 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/app/breakpad_field_trial_win.h"
+
+#include "base/metrics/field_trial.h"
+#include "base/string_util.h"
+#include "base/string16.h"
+#include "base/stringprintf.h"
+#include "breakpad/src/client/windows/common/ipc_protocol.h"
+#include "chrome/app/breakpad_win.h"
+#include "chrome/common/child_process_logging.h"
+
+namespace {
+
+// Allocated in InitExperimentList and destroyed in TermExperimentList.
+base::FieldTrialList* g_field_trial_list = NULL;

[robertshield, 2012/03/23 15:42:10]

Thinking about this a bit more, would a base::LazyInstance be useful here? The
pattern of explicit InitFoo()/TermFoo() calls has proven itself somewhat fragile
in the face of the ever-more complicated Chrome start up and shutdown.

[MAD, 2012/03/23 18:24:23]

Done.
Good idea, I didn't think of it...
Now I will never forget... :-)
Thanks!

+
+}
+
+extern "C" void __declspec(dllexport) __cdecl InitExperimentList(
+    const std::string& state) {
+  DCHECK(!g_field_trial_list);
+  g_field_trial_list = new base::FieldTrialList(EmptyString());
+  base::FieldTrialList::CreateTrialsInChildProcess(state);
+  UpdateExperiments();
+}
+
+extern "C" void __declspec(dllexport) __cdecl AddFieldTrialGroup(
+    const std::string& field_trial_name, const std::string& group_name) {
+  base::FieldTrialList::CreateFieldTrial(field_trial_name, group_name);
+  // TODO(mad): Find a way to just add the |field_trial_name| and |group_name|
+  // instead of starting over each time.
+  UpdateExperiments();
+}
+
+extern "C" void __declspec(dllexport) __cdecl TermExperimentList() {
+  DCHECK(g_field_trial_list);
+  delete g_field_trial_list;
+  g_field_trial_list = NULL;
+}
+
+void UpdateExperiments() {
+  // Make sure we were initialized before we start writing data
+  if (breakpad_win::g_experiment_chunks_offset == 0)
+    return;
+
+  std::vector<base::FieldTrial::NameGroupId> name_group_ids;
+  base::FieldTrialList::GetFieldTrialNameGroupIds(&name_group_ids);
+
+  std::vector<string16> experiment_strings(name_group_ids.size());
+  for (size_t i = 0; i < name_group_ids.size(); ++i) {
+    experiment_strings[i] = base::StringPrintf(
+        L"%x-%x", name_group_ids[i].name, name_group_ids[i].group);
+  }
+
+  size_t num_chunks = 0;
+  size_t current_experiment = 0;
+  string16 current_chunk;
+  // Preallocate the string...
+  current_chunk.resize(google_breakpad::CustomInfoEntry::kValueMaxLength);

[robertshield, 2012/03/23 15:42:10]

The above can be simplified to:
string16 current_chunk(google_breakpad::CustomInfoEntry::kValueMaxLength, 0);

[MAD, 2012/03/23 18:24:23]

Done.

+  current_chunk.erase();  // But start empty... This won't force a realloc.
+  while (current_experiment < experiment_strings.size() &&
+         num_chunks < kMaxReportedExperimentChunks) {
+    // Check if we have enough room to add another experiment to the current
+    // chunk string. If not, we commit the current chunk string and start over.
+    if (current_chunk.size() + experiment_strings[current_experiment].size() >
+        google_breakpad::CustomInfoEntry::kValueMaxLength) {
+      base::wcslcpy(
+          (*breakpad_win::g_custom_entries)[
+              breakpad_win::g_experiment_chunks_offset + num_chunks].value,
+          current_chunk.c_str(),
+          current_chunk.size() + 1);  // This must include the NULL termination.
+      ++num_chunks;
+      current_chunk = experiment_strings[current_experiment];
+    } else {
+      if (!current_chunk.empty())
+        current_chunk += L",";
+      current_chunk += experiment_strings[current_experiment];
+    }
+    ++current_experiment;
+  }
+
+  // Commit the last chunk that didn't get big enough yet.
+  if (!current_chunk.empty() && num_chunks < kMaxReportedExperimentChunks) {
+    base::wcslcpy(
+        (*breakpad_win::g_custom_entries)[
+            breakpad_win::g_experiment_chunks_offset + num_chunks].value,
+        current_chunk.c_str(),
+        current_chunk.size() + 1);  // This must include the NULL termination.
+  }
+
+  // Make note of the total number of experiments,
+  // even if it's > kMaxReportedExperimentChunks. This is useful when
+  // correlating stability with the number of experiments running
+  // simultaneously.
+  base::wcslcpy(
+      (*breakpad_win::g_custom_entries)[
+          breakpad_win::g_num_of_experiments_offset].value,
+      base::StringPrintf(L"%d", name_group_ids.size()).c_str(),
+      google_breakpad::CustomInfoEntry::kValueMaxLength);
+}