Support deserialized compilation of the empty program.

pkg/compiler/lib/src/js_backend/backend.dart

Index: pkg/compiler/lib/src/js_backend/backend.dart
diff --git a/pkg/compiler/lib/src/js_backend/backend.dart b/pkg/compiler/lib/src/js_backend/backend.dart
index 3c29d53801701a35b290d5757e094517f2039ae5..e3e45079553457bb6c3b9b3113c7a548cb572e9f 100644
--- a/pkg/compiler/lib/src/js_backend/backend.dart
+++ b/pkg/compiler/lib/src/js_backend/backend.dart
@@ -511,6 +511,8 @@ class JavaScriptBackend extends Backend {
   final BackendHelpers helpers;
   final BackendImpacts impacts;
 
+  JSFrontendAccess _frontend;
+
   JavaScriptBackend(Compiler compiler,
       {bool generateSourceMap: true,
       bool useStartupEmitter: false,
@@ -545,6 +547,7 @@ class JavaScriptBackend extends Backend {
         ? new CpsFunctionCompiler(compiler, this, sourceInformationStrategy)
         : new SsaFunctionCompiler(this, sourceInformationStrategy);
     serialization = new JavaScriptBackendSerialization(this);
+    _frontend = new JSFrontendAccess(compiler);

[Siggi Cherem (dart-lang), 2016/04/15 15:42:14]

seems it should be possible to make this an initializer and convert _frontend
into a `final frontend` instead

[Johnni Winther, 2016/04/18 08:05:43]

Done.

   }
 
   ConstantSystem get constantSystem => constants.constantSystem;
@@ -2473,6 +2476,35 @@ class JavaScriptBackend extends Backend {
         supportDumpInfo: supportDumpInfo,
         supportSerialization: supportSerialization);
   }
+
+  @override
+  Frontend get frontend => _frontend;
+}
+
+class JSFrontendAccess implements Frontend {
+  final Compiler compiler;
+
+  JSFrontendAccess(this.compiler);
+
+  Resolution get resolution => compiler.resolution;
+
+  @override
+  ResolutionImpact getResolutionImpact(Element element) {
+    return resolution.getResolutionImpact(element);
+  }
+
+  @override
+  ResolvedAst getResolvedAst(Element element) {
+    if (element is SynthesizedCallMethodElementX) {
+      return element.resolvedAst;
+    } else if (element is ConstructorBodyElementX) {
+      return element.resolvedAst;
+    } else {
+      assert(invariant(element, resolution.hasResolvedAst(element.declaration),
+          message: 'No ResolvedAst for $element'));
+      return resolution.getResolvedAst(element.declaration);
+    }
+  }
 }
 
 /// Handling of special annotations for tests.