Add --hide-package-warnings option.

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 6ad363a5072ce7b0172a7a926e6943a484492abd..ffdcc9980e4c8e013dce9048002b5d77da542ba4 100644
--- a/sdk/lib/_internal/compiler/implementation/apiimpl.dart
+++ b/sdk/lib/_internal/compiler/implementation/apiimpl.dart
@@ -62,7 +62,9 @@ class Compiler extends leg.Compiler {
             dumpInfo: hasOption(options, '--dump-info'),
             buildId: extractStringOption(
                 options, '--build-id=',
-                "build number could not be determined")) {
+                "build number could not be determined"),
+            hidePackageWarnings:
+                hasOption(options, '--hide-package-warnings')) {
     if (!libraryRoot.path.endsWith("/")) {
       throw new ArgumentError("libraryRoot must end with a /");
     }