[WIP] Initial CallFunctionCallback builtin.

src/mips64/code-stubs-mips64.cc

Index: src/mips64/code-stubs-mips64.cc
diff --git a/src/mips64/code-stubs-mips64.cc b/src/mips64/code-stubs-mips64.cc
index 1b6b5025226c77253c30694bf551a337305f204f..ab085df503685860bf201055070efab726309683 100644
--- a/src/mips64/code-stubs-mips64.cc
+++ b/src/mips64/code-stubs-mips64.cc
@@ -2797,13 +2797,6 @@ void InternalArrayConstructorStub::Generate(MacroAssembler* masm) {
   GenerateCase(masm, FAST_ELEMENTS);
 }
 
-static int AddressOffset(ExternalReference ref0, ExternalReference ref1) {
-  int64_t offset = (ref0.address() - ref1.address());
-  DCHECK(static_cast<int>(offset) == offset);
-  return static_cast<int>(offset);
-}
-
-
 // Calls an API function.  Allocates HandleScope, extracts returned value
 // from handle and propagates exceptions.  Restores context.  stack_space
 // - space to be unwound on exit (includes the call JS arguments space and
@@ -2914,6 +2907,9 @@ static void CallApiFunctionAndReturn(
   __ Ld(a5, MemOperand(at));
   __ Branch(&promote_scheduled_exception, ne, a4, Operand(a5));
 
+  // Check if the function returned a valid JavaScript value.
+  __ AssertApiCallResult(v0);
+
   __ Ret();
 
   // Re-throw by promoting a scheduled exception.