Store and retrieve features from shared memory

base/feature_list.cc

Index: base/feature_list.cc
diff --git a/base/feature_list.cc b/base/feature_list.cc
index 89b105defc6df0119688cb3b0e708f1b905f36df..47da1bf6575afd707a729edf7468efd06a426d20 100644
--- a/base/feature_list.cc
+++ b/base/feature_list.cc
@@ -12,6 +12,7 @@
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "base/metrics/field_trial.h"
+#include "base/pickle.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
 
@@ -27,6 +28,20 @@ FeatureList* g_instance = nullptr;
 // Tracks whether the FeatureList instance was initialized via an accessor.
 bool g_initialized_from_accessor = false;
 
+const uint32_t kFeatureType = 0x06567CA6 + 1;  // SHA1(FeatureEntry) v1
+
+struct FeatureEntry {
+  // Expected size for 32/64-bit check.
+  static constexpr size_t kExpectedInstanceSize = 8;
+
+  // Specifies whether a feature override enables or disables the future. Same
+  // values as the OverrideState enum in feature_list.h
+  uint32_t override_state;
+
+  // Size of the pickled structure, NOT the total size of this entry.
+  uint32_t size;
+};
+
 // 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
@@ -56,6 +71,23 @@ void FeatureList::InitializeFromCommandLine(
   initialized_from_command_line_ = true;
 }
 
+void FeatureList::InitializeFromSharedMemory(
+    SharedPersistentMemoryAllocator* allocator) {
+  DCHECK(!initialized_);
+
+  SharedPersistentMemoryAllocator::Iterator iter(allocator);
+
+  SharedPersistentMemoryAllocator::Reference ref;
+  while ((ref = iter.GetNextOfType(kFeatureType)) !=
+         SharedPersistentMemoryAllocator::kReferenceNull) {
+    const FeatureEntry* entry =
+        allocator->GetAsObject<const FeatureEntry>(ref, kFeatureType);
+    LOG(ERROR) << entry;
+    // get the field trial, feature name, and overiden state and call
+    // registeroverride here.
+  }
+}
+
 bool FeatureList::IsFeatureOverriddenFromCommandLine(
     const std::string& feature_name,
     OverrideState state) const {
@@ -98,6 +130,35 @@ void FeatureList::RegisterFieldTrialOverride(const std::string& feature_name,
   RegisterOverride(feature_name, override_state, field_trial);
 }
 
+void FeatureList::AddFeaturesToAllocator(
+    FieldTrialList::FieldTrialAllocator* allocator) {
+  DCHECK(initialized_);
+
+  for (const auto& override : overrides_) {
+    Pickle pickle;
+    pickle.WriteString(override.first);
+    if (override.second.field_trial)
+      pickle.WriteString(override.second.field_trial->trial_name());
+
+    size_t total_size = sizeof(FeatureEntry) + pickle.size();
+    SharedPersistentMemoryAllocator::Reference ref =
+        allocator->Allocate(total_size, kFeatureType);
+    if (!ref)
+      return;
+
+    FeatureEntry* entry =
+        allocator->GetAsObject<FeatureEntry>(ref, kFeatureType);
+    entry->override_state = override.second.overridden_state;
+    entry->size = pickle.size();
+
+    char* dst = reinterpret_cast<char*>(entry) + sizeof(FeatureEntry);
+    memcpy(dst, pickle.data(), pickle.size());
+
+    allocator->MakeIterable(ref);
+    // should we add a ref to each feature?
+  }
+}
+
 void FeatureList::GetFeatureOverrides(std::string* enable_overrides,
                                       std::string* disable_overrides) {
   DCHECK(initialized_);