[es6] Reintroduce the instanceof operator in the backends.

src/code-stub-assembler.h

Index: src/code-stub-assembler.h
diff --git a/src/code-stub-assembler.h b/src/code-stub-assembler.h
index d45aaf921ad151957bac443048844a57b39f4674..19b798216f6fe881be4d032cb77e6a55fceb006d 100644
--- a/src/code-stub-assembler.h
+++ b/src/code-stub-assembler.h
@@ -245,6 +245,12 @@ class CodeStubAssembler : public compiler::CodeAssembler {
                         Label* if_found, Label* if_not_found,
                         Label* call_runtime);
 
+  // Instanceof helpers.
+  // ES6 section 7.3.19 OrdinaryHasInstance (C, O)
+  compiler::Node* OrdinaryHasInstance(compiler::Node* context,
+                                      compiler::Node* callable,
+                                      compiler::Node* object);
+
  private:
   compiler::Node* AllocateRawAligned(compiler::Node* size_in_bytes,
                                      AllocationFlags flags,