Create a README and pubspec for the front_end package.

R=scheglov@google.com

Review URL: https://codereview.chromium.org/2436733003 .

pkg/front_end/LICENSE

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+Copyright 2016, the Dart project authors. All rights reserved.
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google Inc. nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

pkg/front_end/README.md

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+# Front end for Dart
+
+This package provides a low-level API for use by compiler back ends that wish to
+implement the Dart language.  It is intended for eventual use by dev_compiler,
+dart2js, and the Dart VM.  In addition, it will share implementation details
+with the analyzer package--this will be accomplished by having the analyzer
+package import (and re-export) parts of this package's private implementation.
+
+End-users should use the [dartanalyzer][analyzercli] command-line tool to
+analyze their Dart code.
+
+Integrators that want to write tools that analyze Dart code should use the
+[analyzer] package.

pkg/front_end/pubspec.yaml

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+name: front_end
+version: 0.1.0
+author: Dart Team <misc@dartlang.org>
+description: Front end for compilation of Dart code.
+homepage: https://github.com/dart-lang/sdk/tree/master/pkg/front_end
+environment:
+  sdk: '>=1.12.0 <2.0.0'
+dependencies:
+  analyzer: '^0.29.0'
+  path: '^1.3.9'
+  source_span: '^1.2.3'