Diagnose compiler crashes.

dart/lib/compiler/implementation/scanner/scanner_task.dart

Index: dart/lib/compiler/implementation/scanner/scanner_task.dart
diff --git a/dart/lib/compiler/implementation/scanner/scanner_task.dart b/dart/lib/compiler/implementation/scanner/scanner_task.dart
index 4f6d2e88bfa203acd4d223bc387a59269d98d708..19a782e778a28104d3640ef7d6464710d812f24d 100644
--- a/dart/lib/compiler/implementation/scanner/scanner_task.dart
+++ b/dart/lib/compiler/implementation/scanner/scanner_task.dart
@@ -91,19 +91,26 @@ class ScannerTask extends CompilerTask {
     Script script = compilationUnit.script;
     Token tokens;
     try {
-      tokens = new StringScanner(script.text).tokenize();
-    } catch (MalformedInputException ex) {
-      Token token;
-      var message;
-      if (ex.position is num) {
-        // TODO(ahe): Always use tokens in MalformedInputException.
-        token = new Token(EOF_INFO, ex.position);
-      } else {
-        token = ex.position;
+      try {
+        tokens = new StringScanner(script.text).tokenize();
+      } catch (MalformedInputException ex) {
+        Token token;
+        var message;
+        if (ex.position is num) {
+          // TODO(ahe): Always use tokens in MalformedInputException.
+          token = new Token(EOF_INFO, ex.position);
+        } else {
+          token = ex.position;
+        }
+        compiler.cancel(ex.message, token: token);
       }
-      compiler.cancel(ex.message, token: token);
+      compiler.dietParser.dietParse(compilationUnit, tokens);
+    } catch (CompilerCancelledException ex) {
+      throw;
+    } catch (var ex) {
+      compiler.unhandledExceptionOnElement(compilationUnit);
+      throw;
     }
-    compiler.dietParser.dietParse(compilationUnit, tokens);
   }
 
   LibraryElement loadLibrary(Uri uri, ScriptTag node) {