extensions: Use V8 Maybe version of GetFunction()

Also use As<v8::Object>() for return value of gin::CreateHandle()
because it should always be an object.

BUG=479065

Review URL: https://codereview.chromium.org/1208333002

Cr-Commit-Position: refs/heads/master@{#336731}
diff --git a/extensions/renderer/v8_helpers.h b/extensions/renderer/v8_helpers.h
index 77e2eb8..012cff8c 100644
--- a/extensions/renderer/v8_helpers.h
+++ b/extensions/renderer/v8_helpers.h
@@ -39,6 +39,13 @@
       .ToLocalChecked();
 }
 
+inline v8::Local<v8::String> ToV8StringUnsafe(
+    v8::Isolate* isolate,
+    const std::string& str,
+    v8::NewStringType string_type = v8::NewStringType::kNormal) {
+  return ToV8StringUnsafe(isolate, str.c_str(), string_type);
+}
+
 // Returns true if |maybe| is both a value, and that value is true.
 inline bool IsTrue(v8::Maybe<bool> maybe) {
   return maybe.IsJust() && maybe.FromJust();