Optimize variation field trial evaluation.

components/variations/processed_study.h

Index: components/variations/processed_study.h
diff --git a/components/variations/processed_study.h b/components/variations/processed_study.h
index f62297953d800de51d6c61399d0de57e81ba065f..c9650fd20371732fde380917e0a2544701d142b0 100644
--- a/components/variations/processed_study.h
+++ b/components/variations/processed_study.h
@@ -29,6 +29,10 @@ class ProcessedStudy {
     return total_probability_;
   }
 
+  bool all_assignments_to_one_group() const {
+    return all_assignments_to_one_group_;
+  }
+
   bool is_expired() const { return is_expired_; }
 
   // Gets the index of the experiment with the given |name|. Returns -1 if no
@@ -47,6 +51,9 @@ class ProcessedStudy {
   // Computed total group probability for the study.
   base::FieldTrial::Probability total_probability_;
 
+  // Whether all assignments are to a single group.
+  bool all_assignments_to_one_group_;
+
   // Whether the study is expired.
   bool is_expired_;
 };