Support add-on 'field trial' records.

components/metrics/persistent_system_profile.h

Index: components/metrics/persistent_system_profile.h
diff --git a/components/metrics/persistent_system_profile.h b/components/metrics/persistent_system_profile.h
index 2f687811bd74abc2f0cccc0fc9bc1f9449a2d92e..ccf35b2650374f5c28e359ef2f5b1eb30d14b816 100644
--- a/components/metrics/persistent_system_profile.h
+++ b/components/metrics/persistent_system_profile.h
@@ -7,6 +7,7 @@
 
 #include <vector>
 
+#include "base/strings/string_piece.h"
 #include "base/threading/thread_checker.h"
 #include "components/metrics/proto/system_profile.pb.h"
 
@@ -38,6 +39,9 @@ class PersistentSystemProfile {
   void SetSystemProfile(const std::string& serialized_profile, bool complete);
   void SetSystemProfile(const SystemProfileProto& profile, bool complete);
 
+  // Records the existence of a field trial.
+  void SetFieldTrial(base::StringPiece trial, base::StringPiece group);

[Alexei Svitkine (slow), 2017/06/28 14:59:01]

Maybe AddFieldTrial? Otherwise the name sounds like there's just one.

[bcwhite, 2017/06/28 16:43:31]

Done.

+
   // Tests if a persistent memory allocator contains an system profile.
   static bool HasSystemProfile(
       const base::PersistentMemoryAllocator& memory_allocator);
@@ -55,6 +59,7 @@ class PersistentSystemProfile {
   enum RecordType : uint8_t {
     kUnusedSpace = 0,  // The default value for empty memory.
     kSystemProfileProto,
+    kFieldTrialInfo,
   };
 
   // A class for managing record allocations inside a persistent memory segment.
@@ -70,7 +75,7 @@ class PersistentSystemProfile {
     // These methods manage writing records to the allocator. Do not mix these
     // with "read" calls; it's one or the other.
     void Reset();
-    bool Write(RecordType type, const std::string& record);
+    bool Write(RecordType type, base::StringPiece record);
 
     // Read a record from the allocator. Do not mix this with "write" calls;
     // it's one or the other.
@@ -114,6 +119,14 @@ class PersistentSystemProfile {
     // Copy and assign are allowed for easy use with STL containers.
   };
 
+  // Write a record to all registered allocators.
+  void WriteToAll(RecordType type, base::StringPiece record);
+
+  // Merges all extension records into a system profile.

[Alexei Svitkine (slow), 2017/06/28 14:59:01]

Update comment too.

[bcwhite, 2017/06/28 16:43:31]

Done.

+  static void MergeUpdateRecords(
+      const base::PersistentMemoryAllocator& memory_allocator,
+      SystemProfileProto* system_profile);
+
   // The list of registered persistent allocators, described by RecordAllocator
   // instances.
   std::vector<RecordAllocator> allocators_;