Introduce "platform configurations" to replace categories and libraries.dart.

pkg/compiler/lib/src/compiler.dart

Index: pkg/compiler/lib/src/compiler.dart
diff --git a/pkg/compiler/lib/src/compiler.dart b/pkg/compiler/lib/src/compiler.dart
index d07dbd2ac867261244381717837b02e13e663d38..271136aa6458e1e724eaf2738bdf6b077ae6c10b 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -929,7 +929,7 @@ abstract class Compiler {
     }
   }
 
-  /// Analyze all member of the library in [libraryUri].
+  /// Analyze all members of the library in [libraryUri].
   ///
   /// If [skipLibraryWithPartOfTag] is `true`, member analysis is skipped if the
   /// library has a `part of` tag, assuming it is a part and not a library.