Add Source.getTextLine and use it to display source snippets in error messages.

pkg/compiler/lib/src/js_emitter/full_emitter/emitter.dart

 // Copyright (c) 2014, 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.
 
 library dart2js.js_emitter.full_emitter;
 
 import 'dart:collection' show HashMap;
 import 'dart:convert';
 
 import 'package:js_runtime/shared/embedded_names.dart' as embeddedNames;
@@ skipping 15 matching lines @@
         FieldElement,
         FunctionElement,
         FunctionSignature,
         LibraryElement,
         MethodElement,
         TypedefElement,
         VariableElement;
 import '../../elements/entities.dart';
 import '../../hash/sha1.dart' show Hasher;
 import '../../io/code_output.dart';
-import '../../io/line_column_provider.dart' show LineColumnCollector;
+import '../../io/location_provider.dart' show LocationCollector;
 import '../../io/source_map_builder.dart' show SourceMapBuilder;
 import '../../js/js.dart' as jsAst;
 import '../../js/js.dart' show js;
 import '../../js_backend/backend_helpers.dart' show BackendHelpers;
 import '../../js_backend/js_backend.dart'
     show
         ConstantEmitter,
         JavaScriptBackend,
         JavaScriptConstantCompiler,
         Namer,
@@ skipping 1469 matching lines @@
               buildConvertGlobalObjectToFastObjects(),
           "debugFastObjects": buildDebugFastObjectCode(),
           "init": buildInitFunction(program.outputContainsConstantList),
           "main": buildMain(mainFragment.invokeMain)
         }));
 
     return new jsAst.Program(statements);
   }
 
   void emitMainOutputUnit(OutputUnit mainOutputUnit, jsAst.Program program) {
-    LineColumnCollector lineColumnCollector;
+    LocationCollector locationCollector;
     List<CodeOutputListener> codeOutputListeners;
     if (generateSourceMap) {
-      lineColumnCollector = new LineColumnCollector();
-      codeOutputListeners = <CodeOutputListener>[lineColumnCollector];
+      locationCollector = new LocationCollector();
+      codeOutputListeners = <CodeOutputListener>[locationCollector];
     }
 
     CodeOutput mainOutput = new StreamCodeOutput(
         compiler.outputProvider('', 'js', OutputType.js), codeOutputListeners);
     outputBuffers[mainOutputUnit] = mainOutput;
 
     mainOutput.addBuffer(jsAst.createCodeBuffer(program, compiler,
         monitor: compiler.dumpInfoTask));
 
     if (compiler.options.deferredMapUri != null) {
       outputDeferredMap();
     }
 
     if (generateSourceMap) {
       mainOutput.add(SourceMapBuilder.generateSourceMapTag(
           compiler.options.sourceMapUri, compiler.options.outputUri));
     }
 
     mainOutput.close();
 
     if (generateSourceMap) {
       SourceMapBuilder.outputSourceMap(
           mainOutput,
-          lineColumnCollector,
+          locationCollector,
           '',
           compiler.options.sourceMapUri,
           compiler.options.outputUri,
           compiler.outputProvider);
     }
   }
 
   Map<OutputUnit, jsAst.Expression> buildDescriptorsForOutputUnits(
       Program program) {
     Map<OutputUnit, jsAst.Expression> outputs =
@@ skipping 282 matching lines @@
   /// itself.
   Map<OutputUnit, String> emitDeferredOutputUnits(
       Map<OutputUnit, jsAst.Program> outputAsts) {
     Map<OutputUnit, String> hunkHashes = new Map<OutputUnit, String>();
 
     for (OutputUnit outputUnit in outputAsts.keys) {
       List<CodeOutputListener> outputListeners = <CodeOutputListener>[];
       Hasher hasher = new Hasher();
       outputListeners.add(hasher);
 
-      LineColumnCollector lineColumnCollector;
+      LocationCollector locationCollector;
       if (generateSourceMap) {
-        lineColumnCollector = new LineColumnCollector();
-        outputListeners.add(lineColumnCollector);
+        locationCollector = new LocationCollector();
+        outputListeners.add(locationCollector);
       }
 
       String partPrefix =
           backend.deferredPartFileName(outputUnit.name, addExtension: false);
       CodeOutput output = new StreamCodeOutput(
           compiler.outputProvider(partPrefix, 'part.js', OutputType.jsPart),
           outputListeners);
 
       outputBuffers[outputUnit] = output;
 
@@ skipping 26 matching lines @@
         if (outputUri != null) {
           String partFileName = partName + ".js";
           List<String> partSegments = outputUri.pathSegments.toList();
           partSegments[partSegments.length - 1] = partFileName;
           partUri =
               compiler.options.outputUri.replace(pathSegments: partSegments);
         }
 
         output.add(SourceMapBuilder.generateSourceMapTag(mapUri, partUri));
         output.close();
-        SourceMapBuilder.outputSourceMap(output, lineColumnCollector, partName,
+        SourceMapBuilder.outputSourceMap(output, locationCollector, partName,
             mapUri, partUri, compiler.outputProvider);
       } else {
         output.close();
       }
 
       hunkHashes[outputUnit] = hash;
     }
     return hunkHashes;
   }
 
@@ skipping 10 matching lines @@
     // data.
     mapping["_comment"] = "This mapping shows which compiled `.js` files are "
         "needed for a given deferred library import.";
     mapping.addAll(compiler.deferredLoadTask.computeDeferredMap());
     compiler.outputProvider(
         compiler.options.deferredMapUri.path, '', OutputType.info)
       ..add(const JsonEncoder.withIndent("  ").convert(mapping))
       ..close();
   }
 }