Re-land: gin: Use V8 Maybe APIs

gin/try_catch.cc

Index: gin/try_catch.cc
diff --git a/gin/try_catch.cc b/gin/try_catch.cc
index 97e7fe15f832b33af9d5648152c2f4986a0f137b..df27b9c1e4f3dc924078ebc65a0128c76c37412c 100644
--- a/gin/try_catch.cc
+++ b/gin/try_catch.cc
@@ -8,9 +8,21 @@
 
 #include "gin/converter.h"
 
+namespace {
+
+v8::Local<v8::String> GetSourceLine(v8::Isolate* isolate,
+                                    v8::Local<v8::Message> message) {
+  auto maybe = message->GetSourceLine(isolate->GetCurrentContext());
+  v8::Local<v8::String> source_line;
+  return maybe.ToLocal(&source_line) ? source_line : v8::String::Empty(isolate);
+}
+
+}  // namespace
+
 namespace gin {
 
-TryCatch::TryCatch() {
+TryCatch::TryCatch(v8::Isolate* isolate)
+    : isolate_(isolate), try_catch_(isolate) {
 }
 
 TryCatch::~TryCatch() {
@@ -28,7 +40,7 @@ std::string TryCatch::GetStackTrace() {
   std::stringstream ss;
   v8::Local<v8::Message> message = try_catch_.Message();
   ss << V8ToString(message->Get()) << std::endl
-     << V8ToString(message->GetSourceLine()) << std::endl;
+     << V8ToString(GetSourceLine(isolate_, message)) << std::endl;
 
   v8::Local<v8::StackTrace> trace = message->GetStackTrace();
   if (trace.IsEmpty())