Store field trial parameters in shared memory

base/metrics/field_trial_param_associator.h

Index: base/metrics/field_trial_param_associator.h
diff --git a/base/metrics/field_trial_param_associator.h b/base/metrics/field_trial_param_associator.h
index 214e146966eebbdf8fe0888f4c705eea1f251fb0..b19c66661c7063035ab3058c6c8634dc2058afe1 100644
--- a/base/metrics/field_trial_param_associator.h
+++ b/base/metrics/field_trial_param_associator.h
@@ -11,6 +11,7 @@
 
 #include "base/base_export.h"
 #include "base/memory/singleton.h"
+#include "base/metrics/field_trial.h"
 #include "base/synchronization/lock.h"
 
 namespace base {
@@ -33,13 +34,26 @@ class BASE_EXPORT FieldTrialParamAssociator {
                                  const std::string& group_name,
                                  const FieldTrialParams& params);
 
-  // Gets the parameters for a field trial and its chosen group.
+  // Gets the parameters for a field trial and its chosen group. If not found in
+  // field_trial_params_, then tries to looks it up in shared memory.
   bool GetFieldTrialParams(const std::string& trial_name,
                            FieldTrialParams* params);
 
-  // Clears the internal field_trial_params_ mapping.
+  // Gets the parameters for a field trial and its chosen group. Does not
+  // fallback to looking it up in shared memory. This should only be used if you
+  // know for sure the params are in the mapping, like if you're in the browser
+  // process, and even then you should probably just use GetFieldTrialParams().

[bcwhite, 2016/11/23 21:03:52]

So...  When _should_ this method be used?

[lawrencewu, 2016/11/23 21:49:20]

Pretty much never, except for where it's currently used (in PickleFieldTrial()).
But since that's in a different module this has to be public.

+  bool GetFieldTrialParamsWithoutFallback(const std::string& trial_name,
+                                          const std::string& group_name,
+                                          FieldTrialParams* params);
+
+  // Clears the internal field_trial_params_ mapping, plus removes all params in
+  // shared memory.
   void ClearAllParamsForTesting();
 
+  // Clears the internal field_trial_params_ mapping.
+  void ClearAllCachedParamsForTesting();
+
  private:
   friend struct DefaultSingletonTraits<FieldTrialParamAssociator>;