Version 3.7.9.

src/x64/lithium-codegen-x64.h

Index: src/x64/lithium-codegen-x64.h
===================================================================
--- src/x64/lithium-codegen-x64.h	(revision 10035)
+++ src/x64/lithium-codegen-x64.h	(working copy)
@@ -269,6 +269,13 @@
                          Label* is_not_object,
                          Label* is_object);
 
+  // Emits optimized code for %_IsString(x).  Preserves input register.
+  // Returns the condition on which a final split to
+  // true and false label should be made, to optimize fallthrough.
+  Condition EmitIsString(Register input,
+                         Register temp1,
+                         Label* is_not_string);
+
   // Emits optimized code for %_IsConstructCall().
   // Caller should branch on equal condition.
   void EmitIsConstructCall(Register temp);