Cache output of dart2js compilations that went wrong on disk.

sdk/lib/_internal/compiler/implementation/dart2js.dart

Index: sdk/lib/_internal/compiler/implementation/dart2js.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/dart2js.dart	(revision 35634)
+++ sdk/lib/_internal/compiler/implementation/dart2js.dart	(working copy)
@@ -365,11 +365,11 @@
 
   compilationDone(String code) {
     if (analyzeOnly) return;
+    writeString(Uri.parse('$out.deps'),
+                getDepsOutput(inputProvider.sourceFiles));
     if (code == null) {
       fail('Compilation failed.');
     }
-    writeString(Uri.parse('$out.deps'),
-                getDepsOutput(inputProvider.sourceFiles));
     diagnosticHandler.info(
          'Compiled ${inputProvider.dartCharactersRead} characters Dart '
          '-> $totalCharactersWritten characters $outputLanguage '