Purge cache when the server removes the policy for an extension.

components/policy/core/common/policy_namespace.h

Index: components/policy/core/common/policy_namespace.h
diff --git a/components/policy/core/common/policy_namespace.h b/components/policy/core/common/policy_namespace.h
index 86dc5866afc5f7b207080626ebd3c636fc401175..838fcb8a3cf745fd3d667b6133dd337e927e51e9 100644
--- a/components/policy/core/common/policy_namespace.h
+++ b/components/policy/core/common/policy_namespace.h
@@ -8,6 +8,7 @@
 #include <string>
 #include <vector>
 
+#include "base/containers/hash_tables.h"
 #include "components/policy/policy_export.h"
 
 namespace policy {
@@ -49,4 +50,18 @@ typedef std::vector<PolicyNamespace> PolicyNamespaceList;
 
 }  // namespace policy
 
+// Define a custom std::hash for PolicyNamespace so that it can be used as
+// a key in hash_maps, and in particular in ScopedPtrHashMaps (which use the
+// default std::hash).
+namespace BASE_HASH_NAMESPACE {
+
+template <>
+struct hash<policy::PolicyNamespace> {
+  std::size_t operator()(const policy::PolicyNamespace& ns) const {
+    return hash<std::string>()(ns.component_id) ^ (1 << ns.domain);
+  }
+};
+
+}  // namespace BASE_HASH_NAMESPACE
+
 #endif  // COMPONENTS_POLICY_CORE_COMMON_POLICY_NAMESPACE_H_