Plumb base::Feature field trial association to renderers.
This CL makes the FeatureList command-line initialization code
support an optional FieldTrial name for each feature that will
be associated with the feature override when specified. Also
changes the code that generates this command-line to also
include this name.
With this change, renderers will be launched with this
association specified on the command-line, so that querying
a Feature in the renderer only that's associated with a field
trial will result in that trial being activated (and sync'd with
the browser process by the existing mechanism).
Depends on:
https://codereview.chromium.org/1471693007
BUG=561077
Review URL: https://codereview.chromium.org/1484483002
Cr-Commit-Position: refs/heads/master@{#362343}
diff --git a/base/feature_list.cc b/base/feature_list.cc
index c06ba8b..104bf08 100644
--- a/base/feature_list.cc
+++ b/base/feature_list.cc
@@ -10,6 +10,7 @@
#include "base/logging.h"
#include "base/metrics/field_trial.h"
#include "base/strings/string_split.h"
+#include "base/strings/string_util.h"
namespace base {
@@ -20,6 +21,16 @@
// have more control over initialization timing. Leaky.
FeatureList* g_instance = nullptr;
+// Some characters are not allowed to appear in feature names or the associated
+// field trial names, as they are used as special characters for command-line
+// serialization. This function checks that the strings are ASCII (since they
+// are used in command-line API functions that require ASCII) and whether there
+// are any reserved characters present, returning true if the string is valid.
+// Only called in DCHECKs.
+bool IsValidFeatureOrFieldTrialName(const std::string& name) {
+ return IsStringASCII(name) && name.find_first_of(",<") == std::string::npos;
+}
+
} // namespace
FeatureList::FeatureList() : initialized_(false) {}
@@ -33,12 +44,8 @@
// Process disabled features first, so that disabled ones take precedence over
// enabled ones (since RegisterOverride() uses insert()).
- for (const auto& feature_name : SplitFeatureListString(disable_features)) {
- RegisterOverride(feature_name, OVERRIDE_DISABLE_FEATURE, nullptr);
- }
- for (const auto& feature_name : SplitFeatureListString(enable_features)) {
- RegisterOverride(feature_name, OVERRIDE_ENABLE_FEATURE, nullptr);
- }
+ RegisterOverridesFromCommandLine(disable_features, OVERRIDE_DISABLE_FEATURE);
+ RegisterOverridesFromCommandLine(enable_features, OVERRIDE_ENABLE_FEATURE);
}
bool FeatureList::IsFeatureOverriddenFromCommandLine(
@@ -91,18 +98,23 @@
disable_overrides->clear();
for (const auto& entry : overrides_) {
+ std::string* target_list = nullptr;
switch (entry.second.overridden_state) {
case OVERRIDE_ENABLE_FEATURE:
- if (!enable_overrides->empty())
- enable_overrides->push_back(',');
- enable_overrides->append(entry.first);
+ target_list = enable_overrides;
break;
case OVERRIDE_DISABLE_FEATURE:
- if (!disable_overrides->empty())
- disable_overrides->push_back(',');
- disable_overrides->append(entry.first);
+ target_list = disable_overrides;
break;
}
+
+ if (!target_list->empty())
+ target_list->push_back(',');
+ target_list->append(entry.first);
+ if (entry.second.field_trial) {
+ target_list->push_back('<');
+ target_list->append(entry.second.field_trial->trial_name());
+ }
}
}
@@ -151,6 +163,7 @@
bool FeatureList::IsFeatureEnabled(const Feature& feature) {
DCHECK(initialized_);
+ DCHECK(IsValidFeatureOrFieldTrialName(feature.name)) << feature.name;
DCHECK(CheckFeatureIdentity(feature)) << feature.name;
auto it = overrides_.find(feature.name);
@@ -168,15 +181,39 @@
return feature.default_state == FEATURE_ENABLED_BY_DEFAULT;
}
-void FeatureList::RegisterOverride(const std::string& feature_name,
+void FeatureList::RegisterOverridesFromCommandLine(
+ const std::string& feature_list,
+ OverrideState overridden_state) {
+ for (const auto& value : SplitFeatureListString(feature_list)) {
+ StringPiece feature_name(value);
+ base::FieldTrial* trial = nullptr;
+
+ // The entry may be of the form FeatureName<FieldTrialName - in which case,
+ // this splits off the field trial name and associates it with the override.
+ std::string::size_type pos = feature_name.find('<');
+ if (pos != std::string::npos) {
+ feature_name.set(value.data(), pos);
+ trial = base::FieldTrialList::Find(value.substr(pos + 1));
+ }
+
+ RegisterOverride(feature_name, overridden_state, trial);
+ }
+}
+
+void FeatureList::RegisterOverride(StringPiece feature_name,
OverrideState overridden_state,
FieldTrial* field_trial) {
DCHECK(!initialized_);
+ if (field_trial) {
+ DCHECK(IsValidFeatureOrFieldTrialName(field_trial->trial_name()))
+ << field_trial->trial_name();
+ }
+
// Note: The semantics of insert() is that it does not overwrite the entry if
// one already exists for the key. Thus, only the first override for a given
// feature name takes effect.
overrides_.insert(std::make_pair(
- feature_name, OverrideEntry(overridden_state, field_trial)));
+ feature_name.as_string(), OverrideEntry(overridden_state, field_trial)));
}
bool FeatureList::CheckFeatureIdentity(const Feature& feature) {
