[cfe] Pass triple-shift flag to scanner.

Fixes https://github.com/dart-lang/sdk/issues/37082

Change-Id: I3aead7432b64433a040d4586623e13d8ac5388ca
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/104004
Reviewed-by: Dan Rubel <danrubel@google.com>
Commit-Queue: Aske Simon Christensen <askesc@google.com>

pkg/front_end/lib/src/fasta/source/source_loader.dart

@@ -104,7 +104,8 @@ import '../parser.dart' show Parser, lengthForToken, offsetForToken;
 
 import '../problems.dart' show internalProblem;
 
-import '../scanner.dart' show ErrorToken, ScannerResult, Token, scan;
+import '../scanner.dart'
+    show ErrorToken, ScannerConfiguration, ScannerResult, Token, scan;
 
 import '../type_inference/interface_resolver.dart' show InterfaceResolver;
 
@@ -200,7 +201,10 @@ class SourceLoader extends Loader<Library> {
       byteCount += rawBytes.length;
     }
 
-    ScannerResult result = scan(bytes, includeComments: includeComments);
+    ScannerResult result = scan(bytes,
+        includeComments: includeComments,
+        configuration: new ScannerConfiguration(
+            enableTripleShift: target.enableTripleShift));
     Token token = result.tokens;
     if (!suppressLexicalErrors) {
       List<int> source = getSource(bytes);