Dynamically load packages for dartdevc tests in test.dart.

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

Index: pkg/dev_compiler/lib/src/compiler/command.dart
diff --git a/pkg/dev_compiler/lib/src/compiler/command.dart b/pkg/dev_compiler/lib/src/compiler/command.dart
index af34e95f711c3490304d9cd70cff1f4cfdcaa5f6..dfce39705c426951ebaa9a5bf0e1d53685a5c4fa 100644
--- a/pkg/dev_compiler/lib/src/compiler/command.dart
+++ b/pkg/dev_compiler/lib/src/compiler/command.dart
@@ -180,8 +180,12 @@ void _compile(ArgResults argResults, AnalyzerOptions analyzerOptions,
     modulePath = path.basenameWithoutExtension(firstOutPath);
   }
 
-  var unit = new BuildUnit(modulePath, libraryRoot, argResults.rest,
-      (source) => _moduleForLibrary(moduleRoot, source, compilerOpts));
+  var unit = new BuildUnit(
+      modulePath,
+      libraryRoot,
+      argResults.rest,
+      (source) =>
+          _moduleForLibrary(moduleRoot, source, analyzerOptions, compilerOpts));
 
   var module = compiler.compile(unit, compilerOpts);
   module.errors.forEach(printFn);
@@ -217,10 +221,15 @@ void _compile(ArgResults argResults, AnalyzerOptions analyzerOptions,
   }
 }
 
-String _moduleForLibrary(
-    String moduleRoot, Source source, CompilerOptions compilerOpts) {
+String _moduleForLibrary(String moduleRoot, Source source,
+    AnalyzerOptions analyzerOptions, CompilerOptions compilerOpts) {
   if (source is InSummarySource) {
     var summaryPath = source.summaryPath;
+
+    if (analyzerOptions.customSummaryModules.containsKey(summaryPath)) {
+      return analyzerOptions.customSummaryModules[summaryPath];
+    }
+
     var ext = '.${compilerOpts.summaryExtension}';
     if (path.isWithin(moduleRoot, summaryPath) && summaryPath.endsWith(ext)) {
       var buildUnitPath =