[deoptimizer] Store frame height as proper Smi

For BuiltinContinuationFrames we stored the frame-height as a plain
value, which did not cause problems because height (in bytes) always
looks like a Smi to the GC. This CL introduces proper Smi encoding.

Bug: v8:7584
Change-Id: I5e3c41c2e576926bbb2bad7dbe0f277cc017b495
Reviewed-on: https://chromium-review.googlesource.com/1000782Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52476}

src/deoptimizer.cc

@@ -1713,7 +1713,7 @@ void Deoptimizer::DoComputeBuiltinContinuation(
   // The delta from the SP to the FP; used to reconstruct SP in
   // Isolate::UnwindAndFindHandler.
   output_frame_offset -= kPointerSize;
-  value = static_cast<intptr_t>(output_frame_size_above_fp);
+  value = reinterpret_cast<intptr_t>(Smi::FromInt(output_frame_size_above_fp));
   output_frame->SetFrameSlot(output_frame_offset, value);
   DebugPrintOutputSlot(value, frame_index, output_frame_offset,
                        "frame height at deoptimization\n");

src/frames.cc

@@ -1223,7 +1223,7 @@ int JavaScriptBuiltinContinuationFrame::ComputeParametersCount() const {
 intptr_t JavaScriptBuiltinContinuationFrame::GetSPToFPDelta() const {
   Address height_slot =
       fp() + BuiltinContinuationFrameConstants::kFrameSPtoFPDeltaAtDeoptimize;
-  intptr_t height = *reinterpret_cast<intptr_t*>(height_slot);
+  intptr_t height = Smi::ToInt(*reinterpret_cast<Smi**>(height_slot));
   return height;
 }