Fix adding duplicate trials to allocator (finally)

base/metrics/field_trial.cc

 // Copyright (c) 2012 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 "base/metrics/field_trial.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/base_switches.h"
@@ skipping 20 matching lines @@
 const char kPersistentStringSeparator = '/';  // Currently a slash.
 
 // Define a marker character to be used as a prefix to a trial name on the
 // command line which forces its activation.
 const char kActivationMarker = '*';
 
 // Use shared memory to communicate field trial (experiment) state. Set to false
 // for now while the implementation is fleshed out (e.g. data format, single
 // shared memory segment). See https://codereview.chromium.org/2365273004/ and
 // crbug.com/653874
 const bool kUseSharedMemoryForFieldTrials = false;

[Alexei Svitkine (slow), 2016/11/21 19:20:10]

This probably conflict with your other CL that flipped this?

 
 // Constants for the field trial allocator.
 const char kAllocatorName[] = "FieldTrialAllocator";
 const uint32_t kFieldTrialType = 0xABA17E13 + 2;  // SHA1(FieldTrialEntry) v2
 
 // We allocate 64 KiB to hold all the field trial data. This should be enough,
 // as currently we use ~8KiB for the field trials, and ~10KiB for experiment
 // parameters (as of 9/11/2016). This also doesn't allocate all 64 KiB at once
 // -- the pages only get mapped to physical memory when they are touched. If the
 // size of the allocated field trials does get larger than 64 KiB, then we will
@@ skipping 303 matching lines @@
 void FieldTrial::FinalizeGroupChoiceImpl(bool is_locked) {
   if (group_ != kNotFinalized)
     return;
   accumulated_group_probability_ = divisor_;
   // Here it's OK to use |kDefaultGroupNumber| since we can't be forced and not
   // finalized.
   DCHECK(!forced_);
   SetGroupChoice(default_group_name_, kDefaultGroupNumber);
 
   // Add the field trial to shared memory.
-  if (kUseSharedMemoryForFieldTrials)
+  if (kUseSharedMemoryForFieldTrials && trial_registered_)
     FieldTrialList::OnGroupFinalized(is_locked, this);
 }
 
 bool FieldTrial::GetActiveGroup(ActiveGroup* active_group) const {
   if (!group_reported_ || !enable_field_trial_)
     return false;
   DCHECK_NE(group_, kNotFinalized);
   active_group->trial_name = trial_name_;
   active_group->group_name = group_name_;
   return true;
@@ skipping 634 matching lines @@
     return;
   }
   AutoLock auto_lock(global_->lock_);
   CHECK(!global_->PreLockedFind(trial->trial_name())) << trial->trial_name();
   trial->AddRef();
   trial->SetTrialRegistered();
   global_->registered_[trial->trial_name()] = trial;
 }
 
 }  // namespace base