Speed up snapshots of *int8lists, by using memmove.

runtime/vm/dart_api_message.cc

Index: runtime/vm/dart_api_message.cc
diff --git a/runtime/vm/dart_api_message.cc b/runtime/vm/dart_api_message.cc
index 123d5352a67b994dbd2891d9939206ba2896b63c..8f089d3764283a13bad31de27fa453042558f801 100644
--- a/runtime/vm/dart_api_message.cc
+++ b/runtime/vm/dart_api_message.cc
@@ -600,12 +600,16 @@ Dart_CObject* ApiMessageReader::ReadInternalVMObject(intptr_t class_id,
       return object;
     }
 
-#define READ_TYPED_DATA(type, ctype)                                           \
-    {                                                                          \
+#define READ_TYPED_DATA_HEADER(type)                                           \
       intptr_t len = ReadSmiValue();                                           \
       Dart_CObject* object =                                                   \
-          AllocateDartCObjectTypedData(Dart_TypedData_k##type, len);     \
+          AllocateDartCObjectTypedData(Dart_TypedData_k##type, len);           \
       AddBackRef(object_id, object, kIsDeserialized);                          \
+
+
+#define READ_TYPED_DATA(type, ctype)                                           \
+    {                                                                          \
+      READ_TYPED_DATA_HEADER(type);                                            \
       if (len > 0) {                                                           \
         ctype* p =                                                             \
             reinterpret_cast<ctype*>(object->value.as_typed_data.values);      \
@@ -617,12 +621,26 @@ Dart_CObject* ApiMessageReader::ReadInternalVMObject(intptr_t class_id,
     }                                                                          \
 
     case kTypedDataInt8ArrayCid:
-    case kExternalTypedDataInt8ArrayCid:
-      READ_TYPED_DATA(Int8, int8_t);
+    case kExternalTypedDataInt8ArrayCid: {
+      READ_TYPED_DATA_HEADER(Int8);
+      if (len > 0) {
+        uint8_t* p =
+            reinterpret_cast<uint8_t*>(object->value.as_typed_data.values);
+        ReadBytes(p, len);
+      }
+      return object;
+    }
 
     case kTypedDataUint8ArrayCid:
-    case kExternalTypedDataUint8ArrayCid:
-      READ_TYPED_DATA(Uint8, uint8_t);
+    case kExternalTypedDataUint8ArrayCid: {
+      READ_TYPED_DATA_HEADER(Uint8);
+      if (len > 0) {
+        uint8_t* p =
+            reinterpret_cast<uint8_t*>(object->value.as_typed_data.values);
+        ReadBytes(p, len);
+      }
+      return object;
+    }
 
     case kTypedDataUint8ClampedArrayCid:
     case kExternalTypedDataUint8ClampedArrayCid: