Support sending and receiving Capability objects from C code.

runtime/vm/snapshot_test.cc

Index: runtime/vm/snapshot_test.cc
diff --git a/runtime/vm/snapshot_test.cc b/runtime/vm/snapshot_test.cc
index c00c0f8b5c7e38d6f1538edc8389055575fdde0b..0c4ccaa5544a3926781ca12a14d2591996fbfe78 100644
--- a/runtime/vm/snapshot_test.cc
+++ b/runtime/vm/snapshot_test.cc
@@ -120,6 +120,9 @@ static void CompareDartCObjects(Dart_CObject* first, Dart_CObject* second) {
                             second->value.as_array.values[i]);
       }
       break;
+    case Dart_CObject_kCapability:
+      EXPECT_EQ(first->value.as_capability.id, second->value.as_capability.id);
+      break;
     default:
       EXPECT(false);
   }
@@ -402,6 +405,38 @@ static uword allocator(intptr_t size) {
 }
 
 
+TEST_CASE(SerializeCapability) {
+  StackZone zone(Isolate::Current());
+
+  // Write snapshot with object content.
+  const Capability& capability = Capability::Handle(Capability::New(12345));
+  uint8_t* buffer;
+  MessageWriter writer(&buffer, &zone_allocator, true);
+  writer.WriteMessage(capability);
+  intptr_t buffer_len = writer.BytesWritten();
+
+  // Read object back from the snapshot.
+  MessageSnapshotReader reader(buffer,
+                               buffer_len,
+                               Isolate::Current(),
+                               zone.GetZone());
+  Capability& obj = Capability::Handle();
+  obj ^= reader.ReadObject();
+
+  EXPECT_STREQ(12345, obj.Id());
+
+  // Read object back from the snapshot into a C structure.
+  ApiNativeScope scope;
+  ApiMessageReader api_reader(buffer, buffer_len, &zone_allocator);
+  Dart_CObject* root = api_reader.ReadMessage();
+  EXPECT_NOTNULL(root);
+  EXPECT_EQ(Dart_CObject_kCapability, root->type);
+  int64_t id = root->value.as_capability.id;
+  EXPECT_EQ(12345, id);
+  CheckEncodeDecodeMessage(root);

[siva, 2015/07/30 19:44:06]

You should probably also have a case similar to this where the writing is done
by ApiMessageWriter.

[turnidge, 2015/07/30 21:04:13]

Yes, that's what CheckEncodeDecodeMessage does.

+}
+
+
 TEST_CASE(SerializeBigint) {
   StackZone zone(Isolate::Current());