Retain elements a finer granularity than library.

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

Index: dart/sdk/lib/_internal/compiler/implementation/dart2js.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/dart2js.dart b/dart/sdk/lib/_internal/compiler/implementation/dart2js.dart
index 54b242baf489777c0a8e3fa220242a7bd3ed32b2..6b24057072bc422b56d77c20a3cdf978ccef8bf4 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/dart2js.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/dart2js.dart
@@ -259,6 +259,7 @@ void compile(List<String> argv) {
     new OptionHandler('--categories=.*', setCategories),
     new OptionHandler('--global-js-name=.*', checkGlobalName),
     new OptionHandler('--disable-type-inference', passThrough),
+    new OptionHandler('--terse', passThrough),
 
     // The following two options must come last.
     new OptionHandler('-.*', (String argument) {
@@ -500,6 +501,10 @@ Supported options:
   --enable-diagnostic-colors
     Add colors to diagnostic messages.
 
+  --terse
+    Emit diagnostics without suggestions for how to get rid of the diagnosed
+    problems.
+
 The following options are only used for compiler development and may
 be removed in a future version: