Make backend and reporter customizable.

pkg/compiler/lib/src/compiler.dart

Index: pkg/compiler/lib/src/compiler.dart
diff --git a/pkg/compiler/lib/src/compiler.dart b/pkg/compiler/lib/src/compiler.dart
index b371ba6b3cc75c4fb83f9b66551e66e66b751141..9477e8af6519711891332db098aa200b58fef218 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -79,13 +79,18 @@ import 'universe/world_impact.dart' show ImpactStrategy, WorldImpact;
 import 'util/util.dart' show Link, Setlet;
 import 'world.dart' show World;
 
+typedef Backend MakeBackendFuncion(Compiler compiler);
+
+typedef CompilerDiagnosticReporter MakeReporterFunction(
+    Compiler compiler, CompilerOptions options);
+
 abstract class Compiler implements LibraryLoaderListener {
   final Stopwatch totalCompileTime = new Stopwatch();
   final IdGenerator idGenerator = new IdGenerator();
   World world;
   Types types;
   _CompilerCoreTypes _coreTypes;
-  _CompilerDiagnosticReporter _reporter;
+  CompilerDiagnosticReporter _reporter;
   _CompilerResolution _resolution;
   ParsingContext _parsingContext;
 
@@ -281,17 +286,23 @@ abstract class Compiler implements LibraryLoaderListener {
   Compiler(
       {CompilerOptions options,
       api.CompilerOutput outputProvider,
-      this.environment: const _EmptyEnvironment()})
+      this.environment: const _EmptyEnvironment(),
+      MakeBackendFuncion makeBackend,
+      MakeReporterFunction makeReporter})
       : this.options = options,
         this.cacheStrategy = new CacheStrategy(options.hasIncrementalSupport),
         this.userOutputProvider = outputProvider == null
             ? const NullCompilerOutput()
             : outputProvider {
     world = new World(this);
+    if (makeReporter != null) {
+      _reporter = makeReporter(this, options);
+    } else {
+      _reporter = new CompilerDiagnosticReporter(this, options);
+    }
+    _resolution = new _CompilerResolution(this);
     // TODO(johnniwinther): Initialize core types in [initializeCoreClasses] and
     // make its field final.
-    _reporter = new _CompilerDiagnosticReporter(this, options);
-    _resolution = new _CompilerResolution(this);
     _coreTypes = new _CompilerCoreTypes(_resolution);
     types = new Types(_resolution);
     tracer = new Tracer(this, this.outputProvider);
@@ -304,7 +315,9 @@ abstract class Compiler implements LibraryLoaderListener {
     // for global dependencies.
     globalDependencies = new GlobalDependencyRegistry(this);
 
-    if (options.emitJavaScript) {
+    if (makeBackend != null) {
+      backend = makeBackend(this);
+    } else if (options.emitJavaScript) {
       js_backend.JavaScriptBackend jsBackend = new js_backend.JavaScriptBackend(
           this,
           generateSourceMap: options.generateSourceMap,
@@ -346,7 +359,7 @@ abstract class Compiler implements LibraryLoaderListener {
       constants = backend.constantCompilerTask,
       deferredLoadTask = new DeferredLoadTask(this),
       mirrorUsageAnalyzerTask = new MirrorUsageAnalyzerTask(this),
-      enqueuer = new EnqueueTask(this),
+      enqueuer = backend.makeEnqueuer(),
       dumpInfoTask = new DumpInfoTask(this),
       reuseLibraryTask = new GenericTask('Reuse library', this),
     ];
@@ -1391,7 +1404,7 @@ class _CompilerCoreTypes implements CoreTypes, CoreClasses {
   }
 }
 
-class _CompilerDiagnosticReporter extends DiagnosticReporter {
+class CompilerDiagnosticReporter extends DiagnosticReporter {
   final Compiler compiler;
   final DiagnosticOptions options;
 
@@ -1406,7 +1419,7 @@ class _CompilerDiagnosticReporter extends DiagnosticReporter {
   /// suppressed for each library.
   Map<Uri, SuppressionInfo> suppressedWarnings = <Uri, SuppressionInfo>{};
 
-  _CompilerDiagnosticReporter(this.compiler, this.options);
+  CompilerDiagnosticReporter(this.compiler, this.options);
 
   Element get currentElement => _currentElement;