[builtins] Fix context for ConstructStub calls into C++.

src/mips64/builtins-mips64.cc

Index: src/mips64/builtins-mips64.cc
diff --git a/src/mips64/builtins-mips64.cc b/src/mips64/builtins-mips64.cc
index f86c1770fe5b2f8bcbeca8348d83796cc3c3868d..07a7030505309903c906863f305e686729ed1191 100644
--- a/src/mips64/builtins-mips64.cc
+++ b/src/mips64/builtins-mips64.cc
@@ -31,6 +31,12 @@ void Builtins::Generate_Adaptor(MacroAssembler* masm,
   // -----------------------------------
   __ AssertFunction(a1);
 
+  // Make sure we operate in the context of the called function (for example
+  // ConstructStubs implemented in C++ will be run in the context of the caller
+  // instead of the callee, due to the way that [[Construct]] is defined for
+  // ordinary functions).
+  __ ld(cp, FieldMemOperand(a1, JSFunction::kContextOffset));
+
   // Insert extra arguments.
   int num_extra_args = 0;
   switch (extra_args) {