Fix builds of FLX bundles using AOT compilation (#6684)

packages/flutter_tools/bin/fuchsia_builder.dart

@@ -42,12 +42,12 @@ Future<Null> main(List<String> args) async {
   }
   Cache.flutterRoot = Platform.environment['FLUTTER_ROOT'];
   String outputPath = argResults[_kOptionOutput];
-  final int buildResult = await build(
+  final int buildResult = await assemble(
     outputPath: outputPath,
-    snapshotPath: argResults[_kOptionSnapshot],
+    snapshotFile: new File(argResults[_kOptionSnapshot]),
     workingDirPath: argResults[_kOptionWorking],
     packagesPath: argResults[_kOptionPackages],
-    precompiledSnapshot: true,
+    manifestPath: defaultManifestPath,
     includeRobotoFonts: true,
   );
   if (buildResult != 0) {

packages/flutter_tools/lib/src/flx.dart

@@ -90,6 +90,7 @@ Future<int> build({
   depfilePath ??= defaultDepfilePath;
   workingDirPath ??= getAssetBuildDirectory();
   packagesPath ??= path.absolute(PackageMap.globalPackagesPath);
+  File snapshotFile;
 
   if (!precompiledSnapshot) {
     ensureDirectoryExists(snapshotPath);
@@ -107,9 +108,9 @@ Future<int> build({
       printError('Failed to run the Flutter compiler. Exit code: $result');
       return result;
     }
-  }
 
-  File snapshotFile = new File(snapshotPath);
+    snapshotFile = new File(snapshotPath);
+  }
 
   return assemble(
     manifestPath: manifestPath,