Allow a single translation to be from multiple differently-named sources

pkg/intl/test/message_extraction/foo_messages_de_DE.dart

Index: pkg/intl/test/message_extraction/foo_messages_de_DE.dart
diff --git a/pkg/intl/test/message_extraction/foo_messages_de_DE.dart b/pkg/intl/test/message_extraction/foo_messages_de_DE.dart
index b561a3cdcd0c9398f417129f08d28696f4583393..e6866851f25c58fe30a6cbeefd18cb6a856a51c1 100644
--- a/pkg/intl/test/message_extraction/foo_messages_de_DE.dart
+++ b/pkg/intl/test/message_extraction/foo_messages_de_DE.dart
@@ -16,6 +16,8 @@ class MessageLookup extends MessageLookupByLibrary {
   get localeName => 'de_DE';
   static alwaysTranslated() => "Diese Zeichenkette wird immer übersetzt";
 
+  static differentNameSameContents() => "Hallo Welt";
+
   static escapable() => "Escapes: \n\r\f\b\t\v.";
 
   static leadingQuotes() => "\"Sogenannt\"";
@@ -50,6 +52,8 @@ class MessageLookup extends MessageLookupByLibrary {
 
   static plurals(num) => "${Intl.plural(num, zero: 'Ist Null Plural?', one: 'Dies ist einmalig', other: 'Dies ist Plural ($num).')}";
 
+  static sameContentsDifferentName() => "Hallo Welt";
+
   static staticMessage() => "Dies ergibt sich aus einer statischen Methode";
 
   static trickyInterpolation(s) => "Interpolation ist schwierig, wenn es einen Satz wie dieser endet ${s}.";
@@ -61,6 +65,7 @@ class MessageLookup extends MessageLookupByLibrary {
 
   final messages = const {
     "alwaysTranslated" : alwaysTranslated,
+    "differentNameSameContents" : differentNameSameContents,
     "escapable" : escapable,
     "leadingQuotes" : leadingQuotes,
     "message1" : message1,
@@ -78,6 +83,7 @@ class MessageLookup extends MessageLookupByLibrary {
     "outerSelect" : outerSelect,
     "pluralThatFailsParsing" : pluralThatFailsParsing,
     "plurals" : plurals,
+    "sameContentsDifferentName" : sameContentsDifferentName,
     "staticMessage" : staticMessage,
     "trickyInterpolation" : trickyInterpolation,
     "types" : types,