Replace factory constructor with a static method for creating IncrementalKernelGenerator.

pkg/front_end/test/incremental_kernel_generator_test.dart

Index: pkg/front_end/test/incremental_kernel_generator_test.dart
diff --git a/pkg/front_end/test/incremental_kernel_generator_test.dart b/pkg/front_end/test/incremental_kernel_generator_test.dart
index 80197a200e260e89637d9b535ef7ade8f53e37c4..f9e6846e87f8174a24082da3a5e2d39359066158 100644
--- a/pkg/front_end/test/incremental_kernel_generator_test.dart
+++ b/pkg/front_end/test/incremental_kernel_generator_test.dart
@@ -35,14 +35,14 @@ class IncrementalKernelGeneratorTest {
 
     // TODO(scheglov) Make `.packages` file optional.
 
-    incrementalKernelGenerator = new IncrementalKernelGenerator(
-        entryPoint,
-        new CompilerOptions()
-          ..fileSystem = fileSystem
-          ..strongMode = true
-          ..chaseDependencies = true
-          ..dartLibraries = dartLibraries
-          ..packagesFileUri = Uri.parse('file:///test/.packages'));
+    var compilerOptions = new CompilerOptions()
+      ..fileSystem = fileSystem
+      ..strongMode = true
+      ..chaseDependencies = true
+      ..dartLibraries = dartLibraries
+      ..packagesFileUri = Uri.parse('file:///test/.packages');
+    incrementalKernelGenerator = await IncrementalKernelGenerator.newInstance(
+        compilerOptions, entryPoint);
     return (await incrementalKernelGenerator.computeDelta()).newProgram;
   }