Move global dependencies to BackendUsage

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 be8c3956273957cd9a6ac1390c074eaa92a05f27..b3ca4655f76f79dee598e47310625a9f850aec49 100644
--- a/pkg/compiler/lib/src/js_backend/backend.dart
+++ b/pkg/compiler/lib/src/js_backend/backend.dart
@@ -494,8 +494,7 @@ class JavaScriptBackend extends Target implements EnqueuerListener {
         mirrorsData = new MirrorsData(compiler),
         this.compiler = compiler {
     helpers = new BackendHelpers(compiler.elementEnvironment, commonElements);
-    _backendUsage = new BackendUsage(
-        commonElements, helpers, resolution, compiler.globalDependencies);
+    _backendUsage = new BackendUsage(commonElements, helpers, resolution);
     _checkedModeHelpers = new CheckedModeHelpers(commonElements, helpers);
     emitter =
         new CodeEmitterTask(compiler, generateSourceMap, useStartupEmitter);
@@ -933,7 +932,11 @@ class JavaScriptBackend extends Target implements EnqueuerListener {
     return impactBuilder;
   }
 
-  void registerInstantiatedType(ResolutionInterfaceType type) {
+  void registerInstantiatedType(ResolutionInterfaceType type,
+      {bool isGlobal: false}) {
+    if (isGlobal) {
+      backendUsage.registerGlobalDependency(type.element);
+    }
     lookupMapAnalysis.registerInstantiatedType(type);
   }