Dart: Uses a pre-allocated buffer for message pipe query and read.

mojo/dart/embedder/mojo_dart_state.h

Index: mojo/dart/embedder/mojo_dart_state.h
diff --git a/mojo/dart/embedder/mojo_dart_state.h b/mojo/dart/embedder/mojo_dart_state.h
index 6965aa35ef154c7a1ffc355dc38d9a964afd1a6f..e08218b13f9a66d0c0638db5ddc2b61fae8efa42 100644
--- a/mojo/dart/embedder/mojo_dart_state.h
+++ b/mojo/dart/embedder/mojo_dart_state.h
@@ -7,6 +7,7 @@
 
 #include <set>
 #include <string>
+#include <vector>
 
 #include "base/callback.h"
 #include "base/macros.h"
@@ -44,9 +45,9 @@ class MojoDartState : public tonic::DartState {
   const IsolateCallbacks& callbacks() const { return callbacks_; }
   const std::string& script_uri() const { return script_uri_; }
   const std::string& package_root() const { return package_root_; }
-  std::set<MojoHandle>& unclosed_handles() {
-    return unclosed_handles_;
-  }
+  std::set<MojoHandle>& unclosed_handles() { return unclosed_handles_; }
+  std::vector<uint8_t>& message_data() { return message_data_; }
+  std::vector<uint32_t>& message_handles() { return message_handles_; }
 
   const std::set<MojoHandle>& unclosed_handles() const {
     return unclosed_handles_;
@@ -103,6 +104,10 @@ class MojoDartState : public tonic::DartState {
   std::set<MojoHandle> unclosed_handles_;
   std::unique_ptr<tonic::DartLibraryProvider> library_provider_;
   mojo::NetworkServicePtr network_service_;
+
+  // Buffers for sending/receiving messages.
+  std::vector<uint8_t> message_data_;
+  std::vector<uint32_t> message_handles_;
 };
 
 }  // namespace dart