feat(dart/transform): Inline templateUrl values

Modify DirectiveProcessor to inline `templateUrl` values to avoid making
additional browser requests.

Closes #1035

modules/angular2/src/transform/common/async_string_writer.dart

@@ -0,0 +1,75 @@
+library angular2.transform.common.async_string_writer;
+
+import 'dart:async';
+import 'package:analyzer/src/generated/java_core.dart';
+
+/// [PrintWriter] implementation that allows asynchronous printing via
+/// [asyncPrint] and [asyncToString]. See those methods for details.
+class AsyncStringWriter extends PrintWriter {
+  /// All [Future]s we are currently waiting on.
+  final List<Future<String>> _toAwait = <Future<String>>[];
+  final List<StringBuffer> _bufs;
+  StringBuffer _curr;
+  int _asyncCount = 0;
+
+  AsyncStringWriter._(StringBuffer curr)
+      : _curr = curr,
+        _bufs = <StringBuffer>[curr];
+
+  AsyncStringWriter() : this._(new StringBuffer());
+
+  void print(x) {
+    _curr.write(x);
+  }
+
+  /// Adds the result of `futureText` to the writer at the current position
+  /// in the string being built. If using this method, you must use
+  /// [asyncToString] instead of [toString] to get the value of the writer or
+  /// your string may not appear as expected.
+  Future<String> asyncPrint(Future<String> futureText) {
+    _semaphoreIncrement();
+    var myBuf = new StringBuffer();
+    _bufs.add(myBuf);
+    _curr = new StringBuffer();
+    _bufs.add(_curr);
+
+    var toAwait = futureText.then((val) {
+      myBuf.write(val);
+      return val;
+    });
+    _toAwait.add(toAwait);
+    return toAwait.whenComplete(() {
+      _semaphoreDecrementAndCleanup();
+      _toAwait.remove(toAwait);
+    });
+  }
+
+  /// Waits for any values added via [asyncPrint] and returns the fully
+  /// built string.
+  Future<String> asyncToString() {
+    _semaphoreIncrement();
+    var bufLen = _bufs.length;
+    return Future.wait(_toAwait).then((_) {
+      return _bufs.sublist(0, bufLen).join('');
+    }).whenComplete(_semaphoreDecrementAndCleanup);
+  }
+
+  String toString() => _bufs.map((buf) => '$buf').join('(async gap)');
+
+  void _semaphoreIncrement() {
+    ++_asyncCount;
+  }
+
+  void _semaphoreDecrementAndCleanup() {
+    assert(_asyncCount > 0);
+
+    --_asyncCount;
+    if (_asyncCount == 0) {
+      _curr = _bufs[0];
+      for (var i = 1; i < _bufs.length; ++i) {
+        _curr.write('${_bufs[i]}');
+      }
+      _bufs.removeRange(1, _bufs.length);
+    }
+  }
+}

modules/angular2/src/transform/common/xhr_impl.dart

@@ -0,0 +1,25 @@
+library angular2.transform.template_compiler.xhr_impl;
+
+import 'dart:async';
+import 'package:angular2/src/services/xhr.dart' show XHR;
+import 'package:angular2/src/transform/common/asset_reader.dart';
+import 'package:angular2/src/transform/common/logging.dart';
+import 'package:barback/barback.dart';
+import 'package:code_transformers/assets.dart';
+
+class XhrImpl implements XHR {
+  final AssetReader _reader;
+  final AssetId _entryPoint;
+
+  XhrImpl(this._reader, this._entryPoint);
+
+  Future<String> get(String url) async {
+    var assetId = uriToAssetId(_entryPoint, url, logger, null);
+    var templateExists = await _reader.hasInput(assetId);
+    if (!templateExists) {
+      logger.error('Could not read template at uri $url from $_entryPoint');
+      return null;
+    }
+    return await _reader.readAsString(assetId);
+  }
+}