Fix for issue 23598, add a Dart_CreateLibrarySnapshot entrypoint to the API.

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 6707566f534756675fd1bd4f27eabab5aa754b5a..5c9a28a5d3c739105a5d6abe4595042a78dbbbd6 100644
--- a/runtime/vm/snapshot_test.cc
+++ b/runtime/vm/snapshot_test.cc
@@ -1253,6 +1253,8 @@ UNIT_TEST_CASE(ScriptSnapshot) {
   }
 
   FLAG_load_deferred_eagerly = saved_load_deferred_eagerly_mode;
+
+  // Test for Dart_CreateScriptSnapshot.
   {
     // Create an Isolate using the full snapshot, load a script and create
     // a script snapshot of the script.
@@ -1310,8 +1312,50 @@ UNIT_TEST_CASE(ScriptSnapshot) {
     result = Dart_Invoke(cls, NewString("testMain"), 0, NULL);
     EXPECT_VALID(result);
     Dart_ExitScope();
+    Dart_ShutdownIsolate();
+  }
+  free(script_snapshot);
+
+  // Test for Dart_CreateLibrarySnapshot.
+  {
+    // Create an Isolate using the full snapshot, load a script and create
+    // a script snapshot of the script.
+    TestCase::CreateTestIsolateFromSnapshot(full_snapshot);
+    Dart_EnterScope();  // Start a Dart API scope for invoking API functions.
+
+    // Load the library.
+    Dart_Handle lib = Dart_LoadLibrary(NewString("dart_lib"),
+                                       NewString(kScriptChars),
+                                       0, 0);
+    EXPECT_VALID(lib);
+
+    // Write out the script snapshot.
+    result = Dart_CreateLibrarySnapshot(lib, &buffer, &size);
+    EXPECT_VALID(result);
+    script_snapshot = reinterpret_cast<uint8_t*>(malloc(size));
+    memmove(script_snapshot, buffer, size);
+    Dart_ExitScope();
+    Dart_ShutdownIsolate();
+  }
+
+  {
+    // Now Create an Isolate using the full snapshot and load the
+    // script snapshot created above and execute it.
+    TestCase::CreateTestIsolateFromSnapshot(full_snapshot);
+    Dart_EnterScope();  // Start a Dart API scope for invoking API functions.
+
+    // Load the test library from the snapshot.
+    EXPECT(script_snapshot != NULL);
+    result = Dart_LoadScriptFromSnapshot(script_snapshot, size);
+    EXPECT_VALID(result);
+
+    // Invoke a function which returns an object.
+    Dart_Handle cls = Dart_GetClass(result, NewString("FieldsTest"));
+    result = Dart_Invoke(cls, NewString("testMain"), 0, NULL);
+    EXPECT_VALID(result);
+    Dart_ExitScope();
+    Dart_ShutdownIsolate();
   }
-  Dart_ShutdownIsolate();
   free(full_snapshot);
   free(script_snapshot);
 }