Improved support for objects inside persistent memory.

base/metrics/field_trial.h

Index: base/metrics/field_trial.h
diff --git a/base/metrics/field_trial.h b/base/metrics/field_trial.h
index 5ea09484c911660ce56593bd803e1d8d2e616759..5c5240c42af6bc4ba773f1c2d1fdec21e1179ce1 100644
--- a/base/metrics/field_trial.h
+++ b/base/metrics/field_trial.h
@@ -137,9 +137,11 @@ class BASE_EXPORT FieldTrial : public RefCounted<FieldTrial> {
 
   // We create one FieldTrialEntry per field trial in shared memory, via
   // AddToAllocatorWhileLocked. The FieldTrialEntry is followed by a
-  // base::Pickle object that we unpickle and read from. Any changes to this
-  // structure requires a bump in kFieldTrialType id defined in the .cc file.
+  // base::Pickle object that we unpickle and read from.
   struct BASE_EXPORT FieldTrialEntry {
+    // SHA1(FieldTrialEntry): Increment this if structure changes!
+    static constexpr uint32_t kPersistentTypeId = 0xABA17E13 + 2;
+
     // Expected size for 32/64-bit check.
     static constexpr size_t kExpectedInstanceSize = 8;