Move Iterable implementation to collection.

sdk/lib/_internal/compiler/implementation/scanner/token.dart

Index: sdk/lib/_internal/compiler/implementation/scanner/token.dart
diff --git a/sdk/lib/_internal/compiler/implementation/scanner/token.dart b/sdk/lib/_internal/compiler/implementation/scanner/token.dart
index fcf4e871b23b307dc6ae772aeca439e9e6a37bd7..23b4f7832379d3d728e67d2c41070872890bec0e 100644
--- a/sdk/lib/_internal/compiler/implementation/scanner/token.dart
+++ b/sdk/lib/_internal/compiler/implementation/scanner/token.dart
@@ -185,7 +185,7 @@ class StringToken extends Token {
   String slowToString() => value.slowToString();
 }
 
-abstract class SourceString extends Iterable<int> {
+abstract class SourceString extends IterableBase<int> {
   const factory SourceString(String string) = StringWrapper;
 
   void printOn(StringBuffer sb);
@@ -205,7 +205,7 @@ abstract class SourceString extends Iterable<int> {
   bool isPrivate();
 }
 
-class StringWrapper extends Iterable<int> implements SourceString {
+class StringWrapper extends IterableBase<int> implements SourceString {
   final String stringValue;
 
   const StringWrapper(String this.stringValue);