Change --hide-package-warnings to --show-package-warnings and add hint on suppress warnings.

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

Index: sdk/lib/_internal/compiler/implementation/warnings.dart
diff --git a/sdk/lib/_internal/compiler/implementation/warnings.dart b/sdk/lib/_internal/compiler/implementation/warnings.dart
index 0b33526621d019b5eb476d8fb2fd61344d3807c3..993d82cd9391846fbac60ed447b8941f92802a58 100644
--- a/sdk/lib/_internal/compiler/implementation/warnings.dart
+++ b/sdk/lib/_internal/compiler/implementation/warnings.dart
@@ -1748,6 +1748,15 @@ Please include the following information:
       "known type '#{knownType}' of '#{variableName}'.",
       howToFix: "Try replacing '#{shownType}' with '#{shownTypeSuggestion}'.");
 
+  static const MessageKind HIDDEN_WARNINGS_HINTS = const MessageKind(
+      "#{warnings} warning(s) and #{hints} hint(s) suppressed in #{uri}.");
+
+  static const MessageKind HIDDEN_WARNINGS = const MessageKind(
+      "#{warnings} warning(s) suppressed in #{uri}.");
+
+  static const MessageKind HIDDEN_HINTS = const MessageKind(
+      "#{hints} hint(s) suppressed in #{uri}.");
+
   //////////////////////////////////////////////////////////////////////////////
   // Patch errors start.
   //////////////////////////////////////////////////////////////////////////////