[gin] Add Arguments::GetAll()

gin/arguments.h

Index: gin/arguments.h
diff --git a/gin/arguments.h b/gin/arguments.h
index 99a5d16db21c388dc5dc859301e8deb85cc1c1fd..c0a7bc2171d4fd51d2d794b47038484716a493a4 100644
--- a/gin/arguments.h
+++ b/gin/arguments.h
@@ -81,6 +81,11 @@ class GIN_EXPORT Arguments {
   // dereferencing the handle.
   v8::Local<v8::Value> PeekNext() const;
 
+  // Returns all arguments. Since this doesn't require any conversion, it
+  // cannot fail. This does not rely on or modify the current position in the
+  // array used by Get/PeekNext().
+  std::vector<v8::Local<v8::Value>> GetAll() const;
+
   void ThrowError() const;
   void ThrowTypeError(const std::string& message) const;