Add visualization for Chrome configuration changes (fixes #3892)

- Add new API to retrieve/observe configuration values.
- cefclient: Add https://tests/config to inspect configuration
  values in real time.

libcef/browser/global_preference_manager_impl.cc

@@ -4,10 +4,28 @@
 
 #include "cef/libcef/browser/global_preference_manager_impl.h"
 
+#include "base/metrics/field_trial_list_including_low_anonymity.h"
+#include "base/strings/string_util.h"
 #include "cef/libcef/browser/context.h"
 #include "cef/libcef/browser/prefs/pref_helper.h"
 #include "cef/libcef/browser/thread_util.h"
+#include "cef/libcef/common/api_version_util.h"
+#include "chrome/browser/about_flags.h"
 #include "chrome/browser/browser_process.h"
+#include "components/flags_ui/pref_service_flags_storage.h"
+#include "components/variations/synthetic_trials_active_group_id_provider.h"
+
+namespace {
+
+std::string GetActiveGroupNameAsString(
+    const base::FieldTrial::ActiveGroup& group) {
+  constexpr std::string_view kNonBreakingHyphenUTF8 = "\xE2\x80\x91";
+  std::string result = group.trial_name + ":" + group.group_name;
+  base::ReplaceChars(result, "-", kNonBreakingHyphenUTF8, &result);
+  return result;
+}
+
+}  // namespace
 
 bool CefGlobalPreferenceManagerImpl::HasPreference(const CefString& name) {
   CEF_REQUIRE_UIT_RETURN(false);
@@ -40,6 +58,77 @@ bool CefGlobalPreferenceManagerImpl::SetPreference(const CefString& name,
                                     value, error);
 }
 
+CefRefPtr<CefRegistration>
+CefGlobalPreferenceManagerImpl::AddPreferenceObserver(
+    const CefString& name,
+    CefRefPtr<CefPreferenceObserver> observer) {
+  CEF_API_REQUIRE_ADDED(CEF_NEXT);
+  CEF_REQUIRE_UIT_RETURN(nullptr);
+  return CefContext::Get()->GetPrefRegistrar()->AddObserver(name, observer);
+}
+
+// static
+void CefPreferenceManager::GetChromeVariationsAsSwitches(
+    std::vector<CefString>& switches) {
+  CEF_API_REQUIRE_ADDED(CEF_NEXT);
+
+  // Verify that the context is in a valid state.
+  if (!CONTEXT_STATE_VALID()) {
+    DCHECK(false) << "context not valid";
+    return;
+  }
+
+  switches.clear();
+
+  // Based on ChromeFeatureListCreator::ConvertFlagsToSwitches().
+
+  flags_ui::PrefServiceFlagsStorage flags_storage(
+      g_browser_process->local_state());
+  base::CommandLine command_line(base::CommandLine::NO_PROGRAM);
+  about_flags::ConvertFlagsToSwitches(&flags_storage, &command_line,
+                                      flags_ui::kNoSentinels);
+
+  for (const auto& arg : command_line.argv()) {
+    if (!arg.empty()) {
+      switches.push_back(arg);
+    }
+  }
+}
+
+// static
+void CefPreferenceManager::GetChromeVariationsAsStrings(
+    std::vector<CefString>& strings) {
+  CEF_API_REQUIRE_ADDED(CEF_NEXT);
+
+  // Verify that the context is in a valid state.
+  if (!CONTEXT_STATE_VALID()) {
+    DCHECK(false) << "context not valid";
+    return;
+  }
+
+  strings.clear();
+
+  // Based on components/webui/version/version_handler_helper.cc
+  // GetVariationsList().
+
+  base::FieldTrial::ActiveGroups active_groups;
+  // Include low anonymity trial groups in the version string, as it is only
+  // displayed locally (and is useful for diagnostics purposes).
+  base::FieldTrialListIncludingLowAnonymity::
+      GetActiveFieldTrialGroupsForTesting(&active_groups);
+
+  for (const auto& group : active_groups) {
+    strings.push_back(GetActiveGroupNameAsString(group));
+  }
+
+  // Synthetic field trials.
+  for (const auto& group :
+       variations::SyntheticTrialsActiveGroupIdProvider::GetInstance()
+           ->GetGroups()) {
+    strings.push_back(GetActiveGroupNameAsString(group.active_group()));
+  }
+}
+
 // static
 CefRefPtr<CefPreferenceManager>
 CefPreferenceManager::GetGlobalPreferenceManager() {