Move PolicySchema and PolicySchemaRegistry to components/policy/.

This facilitates the refactoring of chrome/browser/policy into a layered
component.

Depends on https://codereview.chromium.org/78823004/

BUG=271392

Review URL: https://codereview.chromium.org/78453005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236785 0039d316-1c4b-4281-b951-d872f2087c98

8 files changed, 1021 insertions, 0 deletions

diff --git a/components/components_tests.gyp b/components/components_tests.gyp
index 96d1cd3..2e00f4a 100644
--- a/components/components_tests.gyp
+++ b/components/components_tests.gyp
@@ -173,6 +173,8 @@
               'sources': [
                 'policy/core/common/policy_bundle_unittest.cc',
                 'policy/core/common/policy_map_unittest.cc',
+                'policy/core/common/schema_map_unittest.cc',
+                'policy/core/common/schema_registry_unittest.cc',
                 'policy/core/common/schema_unittest.cc',
               ],
             }],
diff --git a/components/policy.gypi b/components/policy.gypi
index 9c2c34c..165c477 100644
--- a/components/policy.gypi
+++ b/components/policy.gypi
@@ -38,6 +38,10 @@
             'policy/core/common/schema.cc',
             'policy/core/common/schema.h',
             'policy/core/common/schema_internal.h',
+            'policy/core/common/schema_map.cc',
+            'policy/core/common/schema_map.h',
+            'policy/core/common/schema_registry.cc',
+            'policy/core/common/schema_registry.h',
             'policy/policy_export.h',
           ],
         }, {  # configuration_policy==0
diff --git a/components/policy/core/common/schema_map.cc b/components/policy/core/common/schema_map.cc
new file mode 100644
index 0000000..488af8d
--- /dev/null
+++ b/components/policy/core/common/schema_map.cc
@@ -0,0 +1,105 @@
+// Copyright 2013 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 "components/policy/core/common/schema_map.h"
+
+#include "base/values.h"
+#include "components/policy/core/common/policy_bundle.h"
+#include "components/policy/core/common/policy_map.h"
+
+namespace policy {
+
+SchemaMap::SchemaMap() {}
+
+SchemaMap::SchemaMap(DomainMap& map) {
+  map_.swap(map);
+}
+
+SchemaMap::~SchemaMap() {}
+
+const DomainMap& SchemaMap::GetDomains() const {
+  return map_;
+}
+
+const ComponentMap* SchemaMap::GetComponents(PolicyDomain domain) const {
+  DomainMap::const_iterator it = map_.find(domain);
+  return it == map_.end() ? NULL : &it->second;
+}
+
+const Schema* SchemaMap::GetSchema(const PolicyNamespace& ns) const {
+  const ComponentMap* map = GetComponents(ns.domain);
+  if (!map)
+    return NULL;
+  ComponentMap::const_iterator it = map->find(ns.component_id);
+  return it == map->end() ? NULL : &it->second;
+}
+
+void SchemaMap::FilterBundle(PolicyBundle* bundle) const {
+  for (PolicyBundle::iterator it = bundle->begin(); it != bundle->end(); ++it) {
+    // Chrome policies are not filtered, so that typos appear in about:policy.
+    // Everything else gets filtered, so that components only see valid policy.
+    if (it->first.domain == POLICY_DOMAIN_CHROME)
+      continue;
+
+    const Schema* schema = GetSchema(it->first);
+
+    if (!schema) {
+      it->second->Clear();
+      continue;
+    }
+
+    // TODO(joaodasilva): if a component is registered but doesn't have a schema
+    // then its policies aren't filtered. This behavior is enabled to allow a
+    // graceful update of the Legacy Browser Support extension; it'll be removed
+    // in a future release. http://crbug.com/240704
+    if (!schema->valid())
+      continue;
+
+    PolicyMap* map = it->second;
+    for (PolicyMap::const_iterator it_map = map->begin();
+         it_map != map->end();) {
+      const std::string& policy_name = it_map->first;
+      const base::Value* policy_value = it_map->second.value;
+      Schema policy_schema = schema->GetProperty(policy_name);
+      ++it_map;
+      if (!policy_value || !policy_schema.Validate(*policy_value))
+        map->Erase(policy_name);
+    }
+  }
+}
+
+bool SchemaMap::HasComponents() const {
+  for (DomainMap::const_iterator domain = map_.begin();
+       domain != map_.end(); ++domain) {
+    if (domain->first == POLICY_DOMAIN_CHROME)
+      continue;
+    if (!domain->second.empty())
+      return true;
+  }
+  return false;
+}
+
+void SchemaMap::GetChanges(const scoped_refptr<SchemaMap>& older,
+                           PolicyNamespaceList* removed,
+                           PolicyNamespaceList* added) const {
+  GetNamespacesNotInOther(older, added);
+  older->GetNamespacesNotInOther(this, removed);
+}
+
+void SchemaMap::GetNamespacesNotInOther(const SchemaMap* other,
+                                        PolicyNamespaceList* list) const {
+  list->clear();
+  for (DomainMap::const_iterator domain = map_.begin();
+       domain != map_.end(); ++domain) {
+    const ComponentMap& components = domain->second;
+    for (ComponentMap::const_iterator comp = components.begin();
+         comp != components.end(); ++comp) {
+      PolicyNamespace ns(domain->first, comp->first);
+      if (!other->GetSchema(ns))
+        list->push_back(ns);
+    }
+  }
+}
+
+}  // namespace policy
diff --git a/components/policy/core/common/schema_map.h b/components/policy/core/common/schema_map.h
new file mode 100644
index 0000000..e91886e
--- /dev/null
+++ b/components/policy/core/common/schema_map.h
@@ -0,0 +1,65 @@
+// Copyright 2013 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.
+
+#ifndef COMPONENTS_POLICY_CORE_COMMON_SCHEMA_MAP_H_
+#define COMPONENTS_POLICY_CORE_COMMON_SCHEMA_MAP_H_
+
+#include <map>
+#include <string>
+
+#include "base/basictypes.h"
+#include "base/memory/ref_counted.h"
+#include "components/policy/core/common/policy_namespace.h"
+#include "components/policy/core/common/schema.h"
+#include "components/policy/policy_export.h"
+
+namespace policy {
+
+class PolicyBundle;
+
+typedef std::map<std::string, Schema> ComponentMap;
+typedef std::map<PolicyDomain, ComponentMap> DomainMap;
+
+// Contains a mapping of policy namespaces (domain + component ID) to its
+// corresponding Schema.
+class POLICY_EXPORT SchemaMap : public base::RefCountedThreadSafe<SchemaMap> {
+ public:
+  SchemaMap();
+  // Takes ownership of |map| (its contents will be swapped).
+  explicit SchemaMap(DomainMap& map);
+
+  const DomainMap& GetDomains() const;
+
+  const ComponentMap* GetComponents(PolicyDomain domain) const;
+
+  const Schema* GetSchema(const PolicyNamespace& ns) const;
+
+  // Removes all the policies in |bundle| that don't match the known schemas.
+  // Unknown components are also dropped.
+  void FilterBundle(PolicyBundle* bundle) const;
+
+  // Returns true if this map contains at least one component of a domain other
+  // than POLICY_DOMAIN_CHROME.
+  bool HasComponents() const;
+
+  void GetChanges(const scoped_refptr<SchemaMap>& older,
+                  PolicyNamespaceList* removed,
+                  PolicyNamespaceList* added) const;
+
+ private:
+  friend class base::RefCountedThreadSafe<SchemaMap>;
+
+  void GetNamespacesNotInOther(const SchemaMap* other,
+                               PolicyNamespaceList* list) const;
+
+  ~SchemaMap();
+
+  DomainMap map_;
+
+  DISALLOW_COPY_AND_ASSIGN(SchemaMap);
+};
+
+}  // namespace policy
+
+#endif  // COMPONENTS_POLICY_CORE_COMMON_SCHEMA_MAP_H_
diff --git a/components/policy/core/common/schema_map_unittest.cc b/components/policy/core/common/schema_map_unittest.cc
new file mode 100644
index 0000000..66da2f9
--- /dev/null
+++ b/components/policy/core/common/schema_map_unittest.cc
@@ -0,0 +1,313 @@
+// Copyright 2013 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 "components/policy/core/common/schema_map.h"
+
+#include "base/memory/weak_ptr.h"
+#include "base/values.h"
+#include "components/policy/core/common/external_data_fetcher.h"
+#include "components/policy/core/common/external_data_manager.h"
+#include "components/policy/core/common/policy_bundle.h"
+#include "components/policy/core/common/policy_map.h"
+#include "components/policy/core/common/schema.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace policy {
+
+namespace {
+
+const char kTestSchema[] =
+    "{"
+    "  \"type\": \"object\","
+    "  \"properties\": {"
+    "    \"string\": { \"type\": \"string\" },"
+    "    \"integer\": { \"type\": \"integer\" },"
+    "    \"boolean\": { \"type\": \"boolean\" },"
+    "    \"null\": { \"type\": \"null\" },"
+    "    \"double\": { \"type\": \"number\" },"
+    "    \"list\": {"
+    "      \"type\": \"array\","
+    "      \"items\": { \"type\": \"string\" }"
+    "    },"
+    "    \"object\": {"
+    "      \"type\": \"object\","
+    "      \"properties\": {"
+    "        \"a\": { \"type\": \"string\" },"
+    "        \"b\": { \"type\": \"integer\" }"
+    "      }"
+    "    }"
+    "  }"
+    "}";
+
+}  // namespace
+
+class SchemaMapTest : public testing::Test {
+ protected:
+  Schema CreateTestSchema() {
+    std::string error;
+    Schema schema = Schema::Parse(kTestSchema, &error);
+    if (!schema.valid())
+      ADD_FAILURE() << error;
+    return schema;
+  }
+
+  scoped_refptr<SchemaMap> CreateTestMap() {
+    Schema schema = CreateTestSchema();
+    ComponentMap component_map;
+    component_map["extension-1"] = schema;
+    component_map["extension-2"] = schema;
+    component_map["legacy-extension"] = Schema();
+
+    DomainMap domain_map;
+    domain_map[POLICY_DOMAIN_EXTENSIONS] = component_map;
+
+    return new SchemaMap(domain_map);
+  }
+};
+
+TEST_F(SchemaMapTest, Empty) {
+  scoped_refptr<SchemaMap> map = new SchemaMap();
+  EXPECT_TRUE(map->GetDomains().empty());
+  EXPECT_FALSE(map->GetComponents(POLICY_DOMAIN_CHROME));
+  EXPECT_FALSE(map->GetComponents(POLICY_DOMAIN_EXTENSIONS));
+  EXPECT_FALSE(map->GetSchema(PolicyNamespace(POLICY_DOMAIN_CHROME, "")));
+  EXPECT_FALSE(map->HasComponents());
+}
+
+TEST_F(SchemaMapTest, HasComponents) {
+  scoped_refptr<SchemaMap> map = new SchemaMap();
+  EXPECT_FALSE(map->HasComponents());
+
+  // The Chrome schema does not count as a component.
+  Schema schema = CreateTestSchema();
+  ComponentMap component_map;
+  component_map[""] = schema;
+  DomainMap domain_map;
+  domain_map[POLICY_DOMAIN_CHROME] = component_map;
+  map = new SchemaMap(domain_map);
+  EXPECT_FALSE(map->HasComponents());
+
+  // An extension schema does.
+  domain_map[POLICY_DOMAIN_EXTENSIONS] = component_map;
+  map = new SchemaMap(domain_map);
+  EXPECT_TRUE(map->HasComponents());
+}
+
+TEST_F(SchemaMapTest, Lookups) {
+  scoped_refptr<SchemaMap> map = CreateTestMap();
+  ASSERT_TRUE(map);
+  EXPECT_TRUE(map->HasComponents());
+
+  EXPECT_FALSE(map->GetSchema(
+      PolicyNamespace(POLICY_DOMAIN_CHROME, "")));
+  EXPECT_FALSE(map->GetSchema(
+      PolicyNamespace(POLICY_DOMAIN_CHROME, "extension-1")));
+  EXPECT_FALSE(map->GetSchema(
+      PolicyNamespace(POLICY_DOMAIN_CHROME, "legacy-extension")));
+  EXPECT_FALSE(map->GetSchema(
+      PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "")));
+  EXPECT_FALSE(map->GetSchema(
+      PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "extension-3")));
+
+  const Schema* schema =
+      map->GetSchema(PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "extension-1"));
+  ASSERT_TRUE(schema);
+  EXPECT_TRUE(schema->valid());
+
+  schema = map->GetSchema(
+      PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "legacy-extension"));
+  ASSERT_TRUE(schema);
+  EXPECT_FALSE(schema->valid());
+}
+
+TEST_F(SchemaMapTest, FilterBundle) {
+  std::string error;
+  Schema schema = Schema::Parse(kTestSchema, &error);
+  ASSERT_TRUE(schema.valid()) << error;
+
+  DomainMap domain_map;
+  domain_map[POLICY_DOMAIN_EXTENSIONS]["abc"] = schema;
+  scoped_refptr<SchemaMap> schema_map = new SchemaMap(domain_map);
+
+  PolicyBundle bundle;
+  schema_map->FilterBundle(&bundle);
+  const PolicyBundle empty_bundle;
+  EXPECT_TRUE(bundle.Equals(empty_bundle));
+
+  // The Chrome namespace isn't filtered.
+  PolicyBundle expected_bundle;
+  PolicyNamespace chrome_ns(POLICY_DOMAIN_CHROME, "");
+  expected_bundle.Get(chrome_ns).Set("ChromePolicy",
+                                     POLICY_LEVEL_MANDATORY,
+                                     POLICY_SCOPE_USER,
+                                     base::Value::CreateStringValue("value"),
+                                     NULL);
+  bundle.CopyFrom(expected_bundle);
+
+  // Unknown components are filtered out.
+  PolicyNamespace another_extension_ns(POLICY_DOMAIN_EXTENSIONS, "xyz");
+  bundle.Get(another_extension_ns).Set(
+      "AnotherExtensionPolicy",
+      POLICY_LEVEL_MANDATORY,
+      POLICY_SCOPE_USER,
+      base::Value::CreateStringValue("value"),
+      NULL);
+  schema_map->FilterBundle(&bundle);
+  EXPECT_TRUE(bundle.Equals(expected_bundle));
+
+  PolicyNamespace extension_ns(POLICY_DOMAIN_EXTENSIONS, "abc");
+  PolicyMap& map = expected_bundle.Get(extension_ns);
+  base::ListValue list;
+  list.AppendString("a");
+  list.AppendString("b");
+  map.Set("list", POLICY_LEVEL_MANDATORY, POLICY_SCOPE_USER,
+          list.DeepCopy(), NULL);
+  map.Set("boolean", POLICY_LEVEL_MANDATORY, POLICY_SCOPE_USER,
+          base::Value::CreateBooleanValue(true), NULL);
+  map.Set("integer", POLICY_LEVEL_MANDATORY, POLICY_SCOPE_USER,
+          base::Value::CreateIntegerValue(1), NULL);
+  map.Set("null", POLICY_LEVEL_MANDATORY, POLICY_SCOPE_USER,
+          base::Value::CreateNullValue(), NULL);
+  map.Set("double", POLICY_LEVEL_MANDATORY, POLICY_SCOPE_USER,
+          base::Value::CreateDoubleValue(1.2), NULL);
+  base::DictionaryValue dict;
+  dict.SetString("a", "b");
+  dict.SetInteger("b", 2);
+  map.Set("object", POLICY_LEVEL_MANDATORY, POLICY_SCOPE_USER,
+          dict.DeepCopy(), NULL);
+  map.Set("string", POLICY_LEVEL_MANDATORY, POLICY_SCOPE_USER,
+          base::Value::CreateStringValue("value"), NULL);
+
+  bundle.MergeFrom(expected_bundle);
+  bundle.Get(extension_ns).Set("Unexpected",
+                               POLICY_LEVEL_MANDATORY,
+                               POLICY_SCOPE_USER,
+                               base::Value::CreateStringValue("to-be-removed"),
+                               NULL);
+
+  schema_map->FilterBundle(&bundle);
+  EXPECT_TRUE(bundle.Equals(expected_bundle));
+
+  // Mismatched types are also removed.
+  bundle.Clear();
+  PolicyMap& badmap = bundle.Get(extension_ns);
+  badmap.Set("list", POLICY_LEVEL_MANDATORY, POLICY_SCOPE_USER,
+             base::Value::CreateBooleanValue(false), NULL);
+  badmap.Set("boolean", POLICY_LEVEL_MANDATORY, POLICY_SCOPE_USER,
+             base::Value::CreateIntegerValue(0), NULL);
+  badmap.Set("integer", POLICY_LEVEL_MANDATORY, POLICY_SCOPE_USER,
+             base::Value::CreateBooleanValue(false), NULL);
+  badmap.Set("null", POLICY_LEVEL_MANDATORY, POLICY_SCOPE_USER,
+             base::Value::CreateBooleanValue(false), NULL);
+  badmap.Set("double", POLICY_LEVEL_MANDATORY, POLICY_SCOPE_USER,
+             base::Value::CreateBooleanValue(false), NULL);
+  badmap.Set("object", POLICY_LEVEL_MANDATORY, POLICY_SCOPE_USER,
+             base::Value::CreateBooleanValue(false), NULL);
+  badmap.Set("string", POLICY_LEVEL_MANDATORY, POLICY_SCOPE_USER,
+             NULL,
+             new ExternalDataFetcher(base::WeakPtr<ExternalDataManager>(),
+                                     std::string()));
+
+  schema_map->FilterBundle(&bundle);
+  EXPECT_TRUE(bundle.Equals(empty_bundle));
+}
+
+TEST_F(SchemaMapTest, LegacyComponents) {
+  std::string error;
+  Schema schema = Schema::Parse(
+      "{"
+      "  \"type\":\"object\","
+      "  \"properties\": {"
+      "    \"String\": { \"type\": \"string\" }"
+      "  }"
+      "}", &error);
+  ASSERT_TRUE(schema.valid()) << error;
+
+  DomainMap domain_map;
+  domain_map[POLICY_DOMAIN_EXTENSIONS]["with-schema"] = schema;
+  domain_map[POLICY_DOMAIN_EXTENSIONS]["without-schema"] = Schema();
+  scoped_refptr<SchemaMap> schema_map = new SchemaMap(domain_map);
+
+  // |bundle| contains policies loaded by a policy provider.
+  PolicyBundle bundle;
+
+  // Known components with schemas are filtered.
+  PolicyNamespace extension_ns(POLICY_DOMAIN_EXTENSIONS, "with-schema");
+  bundle.Get(extension_ns).Set("String",
+                               POLICY_LEVEL_MANDATORY,
+                               POLICY_SCOPE_USER,
+                               base::Value::CreateStringValue("value 1"),
+                               NULL);
+
+  // Known components without a schema are not filtered.
+  PolicyNamespace without_schema_ns(POLICY_DOMAIN_EXTENSIONS, "without-schema");
+  bundle.Get(without_schema_ns).Set("Schemaless",
+                                    POLICY_LEVEL_MANDATORY,
+                                    POLICY_SCOPE_USER,
+                                    base::Value::CreateStringValue("value 2"),
+                                    NULL);
+
+  // The Chrome namespace isn't filtered.
+  PolicyNamespace chrome_ns(POLICY_DOMAIN_CHROME, "");
+  bundle.Get(chrome_ns).Set("ChromePolicy",
+                            POLICY_LEVEL_MANDATORY,
+                            POLICY_SCOPE_USER,
+                            base::Value::CreateStringValue("value 3"),
+                            NULL);
+
+  PolicyBundle expected_bundle;
+  expected_bundle.MergeFrom(bundle);
+
+  // Unknown policies of known components with a schema are removed.
+  bundle.Get(extension_ns).Set("Surprise",
+                               POLICY_LEVEL_MANDATORY,
+                               POLICY_SCOPE_USER,
+                               base::Value::CreateStringValue("value 4"),
+                               NULL);
+
+  // Unknown components are removed.
+  PolicyNamespace unknown_ns(POLICY_DOMAIN_EXTENSIONS, "unknown");
+  bundle.Get(unknown_ns).Set("Surprise",
+                             POLICY_LEVEL_MANDATORY,
+                             POLICY_SCOPE_USER,
+                             base::Value::CreateStringValue("value 5"),
+                             NULL);
+
+  schema_map->FilterBundle(&bundle);
+  EXPECT_TRUE(bundle.Equals(expected_bundle));
+}
+
+TEST_F(SchemaMapTest, GetChanges) {
+  DomainMap map;
+  map[POLICY_DOMAIN_CHROME][""] = Schema();
+  scoped_refptr<SchemaMap> older = new SchemaMap(map);
+  map[POLICY_DOMAIN_CHROME][""] = Schema();
+  scoped_refptr<SchemaMap> newer = new SchemaMap(map);
+
+  PolicyNamespaceList removed;
+  PolicyNamespaceList added;
+  newer->GetChanges(older, &removed, &added);
+  EXPECT_TRUE(removed.empty());
+  EXPECT_TRUE(added.empty());
+
+  map[POLICY_DOMAIN_CHROME][""] = Schema();
+  map[POLICY_DOMAIN_EXTENSIONS]["xyz"] = Schema();
+  newer = new SchemaMap(map);
+  newer->GetChanges(older, &removed, &added);
+  EXPECT_TRUE(removed.empty());
+  ASSERT_EQ(1u, added.size());
+  EXPECT_EQ(PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "xyz"), added[0]);
+
+  older = newer;
+  map[POLICY_DOMAIN_EXTENSIONS]["abc"] = Schema();
+  newer = new SchemaMap(map);
+  newer->GetChanges(older, &removed, &added);
+  ASSERT_EQ(2u, removed.size());
+  EXPECT_EQ(PolicyNamespace(POLICY_DOMAIN_CHROME, ""), removed[0]);
+  EXPECT_EQ(PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "xyz"), removed[1]);
+  ASSERT_EQ(1u, added.size());
+  EXPECT_EQ(PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "abc"), added[0]);
+}
+
+}  // namespace policy
diff --git a/components/policy/core/common/schema_registry.cc b/components/policy/core/common/schema_registry.cc
new file mode 100644
index 0000000..16f71e5
--- /dev/null
+++ b/components/policy/core/common/schema_registry.cc
@@ -0,0 +1,175 @@
+// Copyright 2013 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 "components/policy/core/common/schema_registry.h"
+
+#include "base/logging.h"
+
+namespace policy {
+
+SchemaRegistry::Observer::~Observer() {}
+
+SchemaRegistry::SchemaRegistry() : schema_map_(new SchemaMap) {
+  for (int i = 0; i < POLICY_DOMAIN_SIZE; ++i)
+    domains_ready_[i] = false;
+#if !defined(ENABLE_EXTENSIONS)
+  domains_ready_[POLICY_DOMAIN_EXTENSIONS] = true;
+#endif
+}
+
+SchemaRegistry::~SchemaRegistry() {}
+
+void SchemaRegistry::RegisterComponent(const PolicyNamespace& ns,
+                                       const Schema& schema) {
+  ComponentMap map;
+  map[ns.component_id] = schema;
+  RegisterComponents(ns.domain, map);
+}
+
+void SchemaRegistry::RegisterComponents(PolicyDomain domain,
+                                        const ComponentMap& components) {
+  // Assume that a schema was updated if the namespace was already registered
+  // before.
+  DomainMap map(schema_map_->GetDomains());
+  for (ComponentMap::const_iterator it = components.begin();
+       it != components.end(); ++it) {
+    map[domain][it->first] = it->second;
+  }
+  schema_map_ = new SchemaMap(map);
+  Notify(true);
+}
+
+void SchemaRegistry::UnregisterComponent(const PolicyNamespace& ns) {
+  DomainMap map(schema_map_->GetDomains());
+  if (map[ns.domain].erase(ns.component_id) != 0) {
+    schema_map_ = new SchemaMap(map);
+    Notify(false);
+  } else {
+    NOTREACHED();
+  }
+}
+
+bool SchemaRegistry::IsReady() const {
+  for (int i = 0; i < POLICY_DOMAIN_SIZE; ++i) {
+    if (!domains_ready_[i])
+      return false;
+  }
+  return true;
+}
+
+void SchemaRegistry::SetReady(PolicyDomain domain) {
+  if (domains_ready_[domain])
+    return;
+  domains_ready_[domain] = true;
+  if (IsReady())
+    FOR_EACH_OBSERVER(Observer, observers_, OnSchemaRegistryReady());
+}
+
+void SchemaRegistry::AddObserver(Observer* observer) {
+  observers_.AddObserver(observer);
+}
+
+void SchemaRegistry::RemoveObserver(Observer* observer) {
+  observers_.RemoveObserver(observer);
+}
+
+void SchemaRegistry::Notify(bool has_new_schemas) {
+  FOR_EACH_OBSERVER(
+      Observer, observers_, OnSchemaRegistryUpdated(has_new_schemas));
+}
+
+bool SchemaRegistry::HasObservers() const {
+  return observers_.might_have_observers();
+}
+
+CombinedSchemaRegistry::CombinedSchemaRegistry()
+    : own_schema_map_(new SchemaMap) {
+  // The combined registry is always ready, since it can always start tracking
+  // another registry that is not ready yet and going from "ready" to "not
+  // ready" is not allowed.
+  for (int i = 0; i < POLICY_DOMAIN_SIZE; ++i)
+    SetReady(static_cast<PolicyDomain>(i));
+}
+
+CombinedSchemaRegistry::~CombinedSchemaRegistry() {}
+
+void CombinedSchemaRegistry::Track(SchemaRegistry* registry) {
+  registries_.insert(registry);
+  registry->AddObserver(this);
+  // Recombine the maps only if the |registry| has any components other than
+  // POLICY_DOMAIN_CHROME.
+  if (registry->schema_map()->HasComponents())
+    Combine(true);
+}
+
+void CombinedSchemaRegistry::Untrack(SchemaRegistry* registry) {
+  registry->RemoveObserver(this);
+  if (registries_.erase(registry) != 0) {
+    if (registry->schema_map()->HasComponents())
+      Combine(false);
+  } else {
+    NOTREACHED();
+  }
+}
+
+void CombinedSchemaRegistry::RegisterComponents(
+    PolicyDomain domain,
+    const ComponentMap& components) {
+  DomainMap map(own_schema_map_->GetDomains());
+  for (ComponentMap::const_iterator it = components.begin();
+       it != components.end(); ++it) {
+    map[domain][it->first] = it->second;
+  }
+  own_schema_map_ = new SchemaMap(map);
+  Combine(true);
+}
+
+void CombinedSchemaRegistry::UnregisterComponent(const PolicyNamespace& ns) {
+  DomainMap map(own_schema_map_->GetDomains());
+  if (map[ns.domain].erase(ns.component_id) != 0) {
+    own_schema_map_ = new SchemaMap(map);
+    Combine(false);
+  } else {
+    NOTREACHED();
+  }
+}
+
+void CombinedSchemaRegistry::OnSchemaRegistryUpdated(bool has_new_schemas) {
+  Combine(has_new_schemas);
+}
+
+void CombinedSchemaRegistry::OnSchemaRegistryReady() {
+  // Ignore.
+}
+
+void CombinedSchemaRegistry::Combine(bool has_new_schemas) {
+  // If two registries publish a Schema for the same component then it's
+  // undefined which version gets in the combined registry.
+  //
+  // The common case is that both registries want policy for the same component,
+  // and the Schemas should be the same; in that case this makes no difference.
+  //
+  // But if the Schemas are different then one of the components is out of date.
+  // In that case the policy loaded will be valid only for one of them, until
+  // the outdated components are updated. This is a known limitation of the
+  // way policies are loaded currently, but isn't a problem worth fixing for
+  // the time being.
+  DomainMap map(own_schema_map_->GetDomains());
+  for (std::set<SchemaRegistry*>::const_iterator reg_it = registries_.begin();
+       reg_it != registries_.end(); ++reg_it) {
+    const DomainMap& reg_domain_map = (*reg_it)->schema_map()->GetDomains();
+    for (DomainMap::const_iterator domain_it = reg_domain_map.begin();
+         domain_it != reg_domain_map.end(); ++domain_it) {
+      const ComponentMap& reg_component_map = domain_it->second;
+      for (ComponentMap::const_iterator comp_it = reg_component_map.begin();
+           comp_it != reg_component_map.end(); ++comp_it) {
+        map[domain_it->first][comp_it->first] = comp_it->second;
+      }
+    }
+  }
+  schema_map_ = new SchemaMap(map);
+  Notify(has_new_schemas);
+}
+
+}  // namespace policy
diff --git a/components/policy/core/common/schema_registry.h b/components/policy/core/common/schema_registry.h
new file mode 100644
index 0000000..5f56589
--- /dev/null
+++ b/components/policy/core/common/schema_registry.h
@@ -0,0 +1,115 @@
+// Copyright 2013 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.
+
+#ifndef COMPONENTS_POLICY_CORE_COMMON_SCHEMA_REGISTRY_H_
+#define COMPONENTS_POLICY_CORE_COMMON_SCHEMA_REGISTRY_H_
+
+#include <set>
+
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+#include "base/memory/ref_counted.h"
+#include "base/observer_list.h"
+#include "base/threading/non_thread_safe.h"
+#include "components/policy/core/common/policy_namespace.h"
+#include "components/policy/core/common/schema.h"
+#include "components/policy/core/common/schema_map.h"
+
+namespace policy {
+
+class SchemaMap;
+
+// Holds the main reference to the current SchemaMap, and allows a list of
+// observers to get notified whenever it is updated.
+// This object is not thread safe and must be used from the owner's thread,
+// usually UI.
+class POLICY_EXPORT SchemaRegistry : public base::NonThreadSafe {
+ public:
+  class POLICY_EXPORT Observer {
+   public:
+    // Invoked whenever schemas are registered or unregistered.
+    // |has_new_schemas| is true if a new component has been registered since
+    // the last update; this allows observers to ignore updates when
+    // components are unregistered but still get a handle to the current map
+    // (e.g. for periodic reloads).
+    virtual void OnSchemaRegistryUpdated(bool has_new_schemas) = 0;
+
+    // Invoked when all policy domains become ready.
+    virtual void OnSchemaRegistryReady() = 0;
+
+   protected:
+    virtual ~Observer();
+  };
+
+  SchemaRegistry();
+  virtual ~SchemaRegistry();
+
+  const scoped_refptr<SchemaMap>& schema_map() const { return schema_map_; }
+
+  // Register a single component.
+  void RegisterComponent(const PolicyNamespace& ns,
+                         const Schema& schema);
+
+  // Register a list of components for a given domain.
+  virtual void RegisterComponents(PolicyDomain domain,
+                                  const ComponentMap& components);
+
+  virtual void UnregisterComponent(const PolicyNamespace& ns);
+
+  // Returns true if all domains have registered the initial components.
+  bool IsReady() const;
+
+  // This indicates that the initial components for |domain| have all been
+  // registered. It must be invoked at least once for each policy domain;
+  // subsequent calls for the same domain are ignored.
+  void SetReady(PolicyDomain domain);
+
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+
+  bool HasObservers() const;
+
+ protected:
+  void Notify(bool has_new_schemas);
+
+  scoped_refptr<SchemaMap> schema_map_;
+
+ private:
+  ObserverList<Observer, true> observers_;
+  bool domains_ready_[POLICY_DOMAIN_SIZE];
+
+  DISALLOW_COPY_AND_ASSIGN(SchemaRegistry);
+};
+
+// A registry that combines the maps of other registries.
+class POLICY_EXPORT CombinedSchemaRegistry : public SchemaRegistry,
+                                             public SchemaRegistry::Observer {
+ public:
+  CombinedSchemaRegistry();
+  virtual ~CombinedSchemaRegistry();
+
+  void Track(SchemaRegistry* registry);
+  void Untrack(SchemaRegistry* registry);
+
+  virtual void RegisterComponents(PolicyDomain domain,
+                                  const ComponentMap& components) OVERRIDE;
+
+  virtual void UnregisterComponent(const PolicyNamespace& ns) OVERRIDE;
+
+  virtual void OnSchemaRegistryUpdated(bool has_new_schemas) OVERRIDE;
+
+  virtual void OnSchemaRegistryReady() OVERRIDE;
+
+ private:
+  void Combine(bool has_new_schemas);
+
+  std::set<SchemaRegistry*> registries_;
+  scoped_refptr<SchemaMap> own_schema_map_;
+
+  DISALLOW_COPY_AND_ASSIGN(CombinedSchemaRegistry);
+};
+
+}  // namespace policy
+
+#endif  // COMPONENTS_POLICY_CORE_COMMON_SCHEMA_REGISTRY_H_
diff --git a/components/policy/core/common/schema_registry_unittest.cc b/components/policy/core/common/schema_registry_unittest.cc
new file mode 100644
index 0000000..94e245e
--- /dev/null
+++ b/components/policy/core/common/schema_registry_unittest.cc
@@ -0,0 +1,242 @@
+// Copyright 2013 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 "components/policy/core/common/schema_registry.h"
+
+#include "components/policy/core/common/policy_namespace.h"
+#include "components/policy/core/common/schema.h"
+#include "testing/gmock/include/gmock/gmock.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+using ::testing::Mock;
+using ::testing::_;
+
+namespace policy {
+
+namespace {
+
+const char kTestSchema[] =
+    "{"
+    "  \"type\": \"object\","
+    "  \"properties\": {"
+    "    \"string\": { \"type\": \"string\" },"
+    "    \"integer\": { \"type\": \"integer\" },"
+    "    \"boolean\": { \"type\": \"boolean\" },"
+    "    \"null\": { \"type\": \"null\" },"
+    "    \"double\": { \"type\": \"number\" },"
+    "    \"list\": {"
+    "      \"type\": \"array\","
+    "      \"items\": { \"type\": \"string\" }"
+    "    },"
+    "    \"object\": {"
+    "      \"type\": \"object\","
+    "      \"properties\": {"
+    "        \"a\": { \"type\": \"string\" },"
+    "        \"b\": { \"type\": \"integer\" }"
+    "      }"
+    "    }"
+    "  }"
+    "}";
+
+class MockSchemaRegistryObserver : public SchemaRegistry::Observer {
+ public:
+  MockSchemaRegistryObserver() {}
+  virtual ~MockSchemaRegistryObserver() {}
+
+  MOCK_METHOD1(OnSchemaRegistryUpdated, void(bool));
+  MOCK_METHOD0(OnSchemaRegistryReady, void());
+};
+
+}  // namespace
+
+TEST(SchemaRegistryTest, Notifications) {
+  std::string error;
+  Schema schema = Schema::Parse(kTestSchema, &error);
+  ASSERT_TRUE(schema.valid()) << error;
+
+  MockSchemaRegistryObserver observer;
+  SchemaRegistry registry;
+  EXPECT_FALSE(registry.HasObservers());
+  registry.AddObserver(&observer);
+  EXPECT_TRUE(registry.HasObservers());
+
+  ASSERT_TRUE(registry.schema_map());
+  EXPECT_FALSE(registry.schema_map()->GetSchema(
+      PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "abc")));
+
+  EXPECT_CALL(observer, OnSchemaRegistryUpdated(true));
+  registry.RegisterComponent(PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "abc"),
+                             schema);
+  Mock::VerifyAndClearExpectations(&observer);
+
+  // Re-register also triggers notifications, because the Schema might have
+  // changed.
+  EXPECT_CALL(observer, OnSchemaRegistryUpdated(true));
+  registry.RegisterComponent(PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "abc"),
+                             schema);
+  Mock::VerifyAndClearExpectations(&observer);
+
+  EXPECT_TRUE(registry.schema_map()->GetSchema(
+      PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "abc")));
+
+  EXPECT_CALL(observer, OnSchemaRegistryUpdated(false));
+  registry.UnregisterComponent(
+      PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "abc"));
+  Mock::VerifyAndClearExpectations(&observer);
+
+  EXPECT_FALSE(registry.schema_map()->GetSchema(
+      PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "abc")));
+
+  // Registering multiple components at once issues only one notification.
+  ComponentMap components;
+  components["abc"] = schema;
+  components["def"] = schema;
+  components["xyz"] = schema;
+  EXPECT_CALL(observer, OnSchemaRegistryUpdated(true));
+  registry.RegisterComponents(POLICY_DOMAIN_EXTENSIONS, components);
+  Mock::VerifyAndClearExpectations(&observer);
+
+  registry.RemoveObserver(&observer);
+  EXPECT_FALSE(registry.HasObservers());
+}
+
+TEST(SchemaRegistryTest, IsReady) {
+  SchemaRegistry registry;
+  MockSchemaRegistryObserver observer;
+  registry.AddObserver(&observer);
+
+  EXPECT_FALSE(registry.IsReady());
+#if defined(ENABLE_EXTENSIONS)
+  EXPECT_CALL(observer, OnSchemaRegistryReady()).Times(0);
+  registry.SetReady(POLICY_DOMAIN_EXTENSIONS);
+  Mock::VerifyAndClearExpectations(&observer);
+  EXPECT_FALSE(registry.IsReady());
+#endif
+  EXPECT_CALL(observer, OnSchemaRegistryReady());
+  registry.SetReady(POLICY_DOMAIN_CHROME);
+  Mock::VerifyAndClearExpectations(&observer);
+  EXPECT_TRUE(registry.IsReady());
+  EXPECT_CALL(observer, OnSchemaRegistryReady()).Times(0);
+  registry.SetReady(POLICY_DOMAIN_CHROME);
+  Mock::VerifyAndClearExpectations(&observer);
+  EXPECT_TRUE(registry.IsReady());
+
+  CombinedSchemaRegistry combined;
+  EXPECT_TRUE(combined.IsReady());
+
+  registry.RemoveObserver(&observer);
+}
+
+TEST(SchemaRegistryTest, Combined) {
+  std::string error;
+  Schema schema = Schema::Parse(kTestSchema, &error);
+  ASSERT_TRUE(schema.valid()) << error;
+
+  MockSchemaRegistryObserver observer;
+  SchemaRegistry registry1;
+  SchemaRegistry registry2;
+  CombinedSchemaRegistry combined;
+  combined.AddObserver(&observer);
+
+  EXPECT_CALL(observer, OnSchemaRegistryUpdated(_)).Times(0);
+  registry1.RegisterComponent(PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "abc"),
+                              schema);
+  Mock::VerifyAndClearExpectations(&observer);
+
+  // Starting to track a registry issues notifications when it comes with new
+  // schemas.
+  EXPECT_CALL(observer, OnSchemaRegistryUpdated(true));
+  combined.Track(&registry1);
+  Mock::VerifyAndClearExpectations(&observer);
+
+  // Adding a new empty registry does not trigger notifications.
+  EXPECT_CALL(observer, OnSchemaRegistryUpdated(_)).Times(0);
+  combined.Track(&registry2);
+  Mock::VerifyAndClearExpectations(&observer);
+
+  // Adding the same component to the combined registry itself triggers
+  // notifications.
+  EXPECT_CALL(observer, OnSchemaRegistryUpdated(true));
+  combined.RegisterComponent(PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "abc"),
+                             schema);
+  Mock::VerifyAndClearExpectations(&observer);
+
+  // Adding components to the sub-registries triggers notifications.
+  EXPECT_CALL(observer, OnSchemaRegistryUpdated(true));
+  registry2.RegisterComponent(PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "def"),
+                              schema);
+  Mock::VerifyAndClearExpectations(&observer);
+
+  // If the same component is published in 2 sub-registries then the combined
+  // registry publishes one of them.
+  EXPECT_CALL(observer, OnSchemaRegistryUpdated(true));
+  registry1.RegisterComponent(PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "def"),
+                              schema);
+  Mock::VerifyAndClearExpectations(&observer);
+
+  ASSERT_EQ(1u, combined.schema_map()->GetDomains().size());
+  ASSERT_TRUE(combined.schema_map()->GetComponents(POLICY_DOMAIN_EXTENSIONS));
+  ASSERT_EQ(
+      2u,
+      combined.schema_map()->GetComponents(POLICY_DOMAIN_EXTENSIONS)->size());
+  EXPECT_TRUE(combined.schema_map()->GetSchema(
+      PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "abc")));
+  EXPECT_TRUE(combined.schema_map()->GetSchema(
+      PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "def")));
+  EXPECT_FALSE(combined.schema_map()->GetSchema(
+      PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "xyz")));
+
+  EXPECT_CALL(observer, OnSchemaRegistryUpdated(false));
+  registry1.UnregisterComponent(
+      PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "abc"));
+  Mock::VerifyAndClearExpectations(&observer);
+  // Still registered at the combined registry.
+  EXPECT_TRUE(combined.schema_map()->GetSchema(
+      PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "abc")));
+
+  EXPECT_CALL(observer, OnSchemaRegistryUpdated(false));
+  combined.UnregisterComponent(
+      PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "abc"));
+  Mock::VerifyAndClearExpectations(&observer);
+  // Now it's gone.
+  EXPECT_FALSE(combined.schema_map()->GetSchema(
+      PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "abc")));
+
+  EXPECT_CALL(observer, OnSchemaRegistryUpdated(false));
+  registry1.UnregisterComponent(
+      PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "def"));
+  Mock::VerifyAndClearExpectations(&observer);
+  // Still registered at registry2.
+  EXPECT_TRUE(combined.schema_map()->GetSchema(
+      PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "def")));
+
+  EXPECT_CALL(observer, OnSchemaRegistryUpdated(false));
+  registry2.UnregisterComponent(
+      PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "def"));
+  Mock::VerifyAndClearExpectations(&observer);
+  // Now it's gone.
+  EXPECT_FALSE(combined.schema_map()->GetSchema(
+      PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "def")));
+
+  EXPECT_CALL(observer, OnSchemaRegistryUpdated(true)).Times(2);
+  registry1.RegisterComponent(PolicyNamespace(POLICY_DOMAIN_CHROME, ""),
+                              schema);
+  registry2.RegisterComponent(PolicyNamespace(POLICY_DOMAIN_EXTENSIONS, "hij"),
+                              schema);
+  Mock::VerifyAndClearExpectations(&observer);
+
+  // Untracking |registry1| doesn't trigger an update nofitication, because it
+  // doesn't contain any components.
+  EXPECT_CALL(observer, OnSchemaRegistryUpdated(_)).Times(0);
+  combined.Untrack(&registry1);
+  Mock::VerifyAndClearExpectations(&observer);
+
+  EXPECT_CALL(observer, OnSchemaRegistryUpdated(false));
+  combined.Untrack(&registry2);
+  Mock::VerifyAndClearExpectations(&observer);
+
+  combined.RemoveObserver(&observer);
+}
+
+}  // namespace policy