Diagnose compiler crashes.

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

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class ScannerTask extends CompilerTask {
   ScannerTask(Compiler compiler) : super(compiler);
   String get name() => 'Scanner';
 
   void scan(CompilationUnitElement compilationUnit) {
     measure(() {
@@ skipping 73 matching lines @@
     }
     if (implicitlyImportCoreLibrary) {
       importLibrary(library, compiler.coreLibrary, null);
     }
   }
 
   void scanElements(CompilationUnitElement compilationUnit) {
     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) {
     bool newLibrary = false;
     LibraryElement library =
       compiler.universe.libraries.putIfAbsent(uri.toString(), () {
           newLibrary = true;
           Script script = compiler.readScript(uri, node);
           LibraryElement element = new LibraryElement(script);
           native.maybeEnableNative(compiler, element, uri);
@@ skipping 81 matching lines @@
   static final int RESOURCE = 4;
 
   /** Next state. */
   static final List<int> NEXT =
       const <int>[NO_TAG_SEEN,
                   IMPORT, // Only one library tag is allowed.
                   IMPORT,
                   SOURCE,
                   RESOURCE];
 }