Add support for big integers to the native message format

runtime/vm/dart_api_message.h

Index: runtime/vm/dart_api_message.h
diff --git a/runtime/vm/dart_api_message.h b/runtime/vm/dart_api_message.h
index b53082a55638ba5fef57e884c1f5d5575d44489e..e0e7c51f1b8519f4c213b4e450a0eedb5ffb1b98 100644
--- a/runtime/vm/dart_api_message.h
+++ b/runtime/vm/dart_api_message.h
@@ -29,6 +29,8 @@ class ApiMessageReader : public BaseReader {
   Dart_CObject* AllocateDartCObjectBool(bool value);
   // Allocates a Dart_CObject object for for a 32-bit integer.
   Dart_CObject* AllocateDartCObjectInt32(int32_t value);
+  // Allocates a Dart_CObject object for bigint data.
+  Dart_CObject* AllocateDartCObjectBigint(intptr_t length);
   // Allocates a Dart_CObject object for a double.
   Dart_CObject* AllocateDartCObjectDouble(double value);
   // Allocates a Dart_CObject object for string data.
@@ -36,6 +38,9 @@ class ApiMessageReader : public BaseReader {
   // Allocates a C array of Dart_CObject objects.
   Dart_CObject* AllocateDartCObjectArray(intptr_t length);
 
+  // Allocate temporary data for the message processing.
+  uint8_t* AllocateTemp(intptr_t size);
+
   void Init();
 
   intptr_t LookupInternalClass(intptr_t class_header);