Allow dart2dart to output one file per library.

sdk/lib/_internal/compiler/implementation/apiimpl.dart

Index: sdk/lib/_internal/compiler/implementation/apiimpl.dart
diff --git a/sdk/lib/_internal/compiler/implementation/apiimpl.dart b/sdk/lib/_internal/compiler/implementation/apiimpl.dart
index a9786cb1cdf5d7ab090901225ac6a3e604733da9..1b174b8e8fa537fb19197562f39a92042b24f918 100644
--- a/sdk/lib/_internal/compiler/implementation/apiimpl.dart
+++ b/sdk/lib/_internal/compiler/implementation/apiimpl.dart
@@ -42,7 +42,9 @@ class Compiler extends leg.Compiler {
             enableMinification: hasOption(options, '--minify'),
             enableNativeLiveTypeAnalysis:
                 !hasOption(options, '--disable-native-live-type-analysis'),
-            emitJavaScript: !hasOption(options, '--output-type=dart'),
+            emitJavaScript: !(hasOption(options, '--output-type=dart') ||
+                              hasOption(options, '--output-type=dart-multi')),
+            dart2dartMultiFile: !hasOption(options, '--output-type=dart'),

[jgruber1, 2014/08/15 06:20:53]

Why the negative logic? If multi-file is not intended to be the default, I think
checking for dart-multi makes more sense.

[sigurdm, 2014/08/15 13:31:42]

Good point.
Done.

             generateSourceMap: !hasOption(options, '--no-source-maps'),
             analyzeAllFlag: hasOption(options, '--analyze-all'),
             analyzeOnly: hasOption(options, '--analyze-only'),