[Turbofan] Add the concept of aliasing to RegisterConfiguration.

test/unittests/compiler/instruction-sequence-unittest.cc

Index: test/unittests/compiler/instruction-sequence-unittest.cc
diff --git a/test/unittests/compiler/instruction-sequence-unittest.cc b/test/unittests/compiler/instruction-sequence-unittest.cc
index ec1bc2a476bf4ab4f6a44757b6365e637c006aed..06f6788f4a37355051bcb28ac795ff3716b752c5 100644
--- a/test/unittests/compiler/instruction-sequence-unittest.cc
+++ b/test/unittests/compiler/instruction-sequence-unittest.cc
@@ -67,8 +67,8 @@ RegisterConfiguration* InstructionSequenceTest::config() {
   if (config_.is_empty()) {
     config_.Reset(new RegisterConfiguration(
         num_general_registers_, num_double_registers_, num_general_registers_,
-        num_double_registers_, num_double_registers_, allocatable_codes,
-        allocatable_double_codes, general_register_names_,
+        num_double_registers_, RegisterConfiguration::OVERLAP,
+        allocatable_codes, allocatable_double_codes, general_register_names_,
         double_register_names_,  // float register names
         double_register_names_));
   }