Fix performance regressions due to lazy initialization.

src/assembler.cc

Index: src/assembler.cc
diff --git a/src/assembler.cc b/src/assembler.cc
index 4944202f076d9817b510dc2aafc28cb7f72f054d..d42fc3c54098254a00552a1808e9a581a64473b9 100644
--- a/src/assembler.cc
+++ b/src/assembler.cc
@@ -112,8 +112,9 @@ struct InitializeDoubleConstants {
   }
 };
 
-static LazyInstance<DoubleConstant, InitializeDoubleConstants>::type
-    double_constants = LAZY_INSTANCE_INITIALIZER;
+static LazyInstance<DoubleConstant, InitializeDoubleConstants,
+    SingleThreadInitOnceTrait>::type double_constants =
+        LAZY_INSTANCE_INITIALIZER;
 
 const char* const RelocInfo::kFillerCommentString = "DEOPTIMIZATION PADDING";