Use a custom Struct for stack trace storage

src/runtime/runtime-internal.cc

Index: src/runtime/runtime-internal.cc
diff --git a/src/runtime/runtime-internal.cc b/src/runtime/runtime-internal.cc
index 5b46b974a5e397758fa65072987b334b6be5a71a..abec8e199e6481fd05e021d14384fc4be69a3242 100644
--- a/src/runtime/runtime-internal.cc
+++ b/src/runtime/runtime-internal.cc
@@ -117,20 +117,26 @@ RUNTIME_FUNCTION(Runtime_ThrowWasmError) {
   Handle<JSObject> error = Handle<JSObject>::cast(error_obj);
   Handle<Object> stack_trace_obj = JSReceiver::GetDataProperty(
       error, isolate->factory()->stack_trace_symbol());
+
   // Patch the stack trace (array of <receiver, function, code, position>).
   if (stack_trace_obj->IsJSArray()) {
+    using ESTF = EncodedStackTraceFrame;
+
     Handle<FixedArray> stack_elements(
         FixedArray::cast(JSArray::cast(*stack_trace_obj)->elements()));
-    DCHECK_EQ(1, stack_elements->length() % 4);
-    DCHECK(Code::cast(stack_elements->get(3))->kind() == Code::WASM_FUNCTION);
-    DCHECK(stack_elements->get(4)->IsSmi() &&
-           Smi::cast(stack_elements->get(4))->value() >= 0);
-    stack_elements->set(4, Smi::FromInt(-1 - byte_offset));
+    DCHECK_EQ(0, stack_elements->length() % ESTF::kElementsPerFrame);
+    DCHECK(Code::cast(stack_elements->get(ESTF::kCodeOffset))->kind() ==
+           Code::WASM_FUNCTION);
+    DCHECK(stack_elements->get(ESTF::kWasmFunctionIndexOffset)->IsSmi() &&
+           Smi::cast(stack_elements->get(ESTF::kWasmFunctionIndexOffset))
+                   ->value() >= 0);
+    stack_elements->set(ESTF::kOffsetOffset, Smi::FromInt(-1 - byte_offset));
   }
-  Handle<Object> detailed_stack_trace_obj = JSReceiver::GetDataProperty(
-      error, isolate->factory()->detailed_stack_trace_symbol());
+
   // Patch the detailed stack trace (array of JSObjects with various
   // properties).
+  Handle<Object> detailed_stack_trace_obj = JSReceiver::GetDataProperty(
+      error, isolate->factory()->detailed_stack_trace_symbol());
   if (detailed_stack_trace_obj->IsJSArray()) {
     Handle<FixedArray> stack_elements(
         FixedArray::cast(JSArray::cast(*detailed_stack_trace_obj)->elements()));