More simplification and unification of frame handling

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index dada993391a42e2fa1a1bbbd293779854493e349..2f4e49656f5ebbd3a6284214e227f3390ab5f6fb 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -1106,8 +1106,8 @@ Object* Isolate::UnwindAndFindHandler() {
       if (offset >= 0) {
         // Compute the stack pointer from the frame pointer. This ensures that
         // argument slots on the stack are dropped as returning would.
-        Address return_sp = frame->fp() -
-                            StandardFrameConstants::kFixedFrameSizeFromFp -
+        Address return_sp = frame->fp() +
+                            StandardFrameConstants::kFixedFrameSizeAboveFp -
                             stack_slots * kPointerSize;
 
         // Gather information from the frame.