Add dart:io stubs to ddc sdk, define dart.library.html

pkg/dev_compiler/lib/src/compiler/compiler.dart

Index: pkg/dev_compiler/lib/src/compiler/compiler.dart
diff --git a/pkg/dev_compiler/lib/src/compiler/compiler.dart b/pkg/dev_compiler/lib/src/compiler/compiler.dart
index ea6764859825648befa346c82d23fb233c04149b..899e18a59e405b8c2ade00284931ab21148f4f10 100644
--- a/pkg/dev_compiler/lib/src/compiler/compiler.dart
+++ b/pkg/dev_compiler/lib/src/compiler/compiler.dart
@@ -97,6 +97,10 @@ class ModuleCompiler {
     options.declaredVariables.forEach(context.declaredVariables.define);
     context.declaredVariables.define('dart.isVM', 'false');
 
+    // TODO(vsm): Should this be hardcoded?
+    context.declaredVariables.define('dart.library.html', 'true');
+    context.declaredVariables.define('dart.library.io', 'false');

[vsm, 2016/12/14 16:20:28]

FYI - I verified that the tests print "html".  Without this, they print "none"
(and still pass).

+
     return new ModuleCompiler.withContext(context, summaryData);
   }