Turn off field trials and reporting of metrics when running benchmarking.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/5628005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@68532 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 32 insertions, 2 deletions

diff --git a/base/metrics/field_trial.cc b/base/metrics/field_trial.cc
index 63d9ed5..d29ed2d 100644
--- a/base/metrics/field_trial.cc
+++ b/base/metrics/field_trial.cc
@@ -17,6 +17,9 @@ const int FieldTrial::kNotParticipating = -1;
 const int FieldTrial::kAllRemainingProbability = -2;
 
 // static
+bool FieldTrial::enable_benchmarking_ = false;
+
+// static
 const char FieldTrialList::kPersistentStringSeparator('/');
 
 static const char kHistogramFieldTrialSeparator('_');
@@ -40,10 +43,13 @@ int FieldTrial::AppendGroup(const std::string& name,
   DCHECK(group_probability <= divisor_);
   DCHECK(group_probability >=0 ||
          group_probability == kAllRemainingProbability);
-  if (group_probability == kAllRemainingProbability)
+  if (group_probability == kAllRemainingProbability) {
     accumulated_group_probability_ = divisor_;
-  else
+  } else {
+    if (enable_benchmarking_)
+      group_probability = 0;
     accumulated_group_probability_ += group_probability;
+  }
   DCHECK(accumulated_group_probability_ <= divisor_);
   if (group_ == kNotParticipating && accumulated_group_probability_ > random_) {
     // This is the group that crossed the random line, so we do the assignment.
@@ -64,6 +70,12 @@ std::string FieldTrial::MakeName(const std::string& name_prefix,
   return big_string.append(FieldTrialList::FindFullName(trial_name));
 }
 
+// static
+void FieldTrial::EnableBenchmarking() {
+  DCHECK_EQ(0u, FieldTrialList::GetFieldTrialCount());
+  enable_benchmarking_ = true;
+}
+
 FieldTrial::~FieldTrial() {}
 
 //------------------------------------------------------------------------------
@@ -190,4 +202,12 @@ bool FieldTrialList::StringAugmentsState(const std::string& prior_state) {
   return true;
 }
 
+// static
+size_t FieldTrialList::GetFieldTrialCount() {
+  if (!global_)
+    return 0;
+  AutoLock auto_lock(global_->lock_);
+  return global_->registered_.size();
+}
+
 }  // namespace base
diff --git a/base/metrics/field_trial.h b/base/metrics/field_trial.h
index 348a1a7..1f0af9e 100644
--- a/base/metrics/field_trial.h
+++ b/base/metrics/field_trial.h
@@ -117,6 +117,9 @@ class FieldTrial : public RefCounted<FieldTrial> {
   static std::string MakeName(const std::string& name_prefix,
                               const std::string& trial_name);
 
+  // Enable benchmarking sets field trials to a common setting.
+  static void EnableBenchmarking();
+
  private:
   friend class RefCounted<FieldTrial>;
 
@@ -148,6 +151,10 @@ class FieldTrial : public RefCounted<FieldTrial> {
   // If this Trial is not a member of an group, this string is empty.
   std::string group_name_;
 
+  // When benchmarking is enabled, field trials all revert to the 'default'
+  // bucket.
+  static bool enable_benchmarking_;
+
   DISALLOW_COPY_AND_ASSIGN(FieldTrial);
 };
 
@@ -206,6 +213,9 @@ class FieldTrialList {
     return TimeTicks::Now();
   }
 
+  // Return the number of active field trials.
+  static size_t GetFieldTrialCount();
+
  private:
   // Helper function should be called only while holding lock_.
   FieldTrial* PreLockedFind(const std::string& name);