Add include_tags and exclude_tags config fields.

doc/package_config.md

 Each package may include a configuration file that applies to the package as a
 whole. This file can be used to provide custom defaults for various options, to
 define configuration for multiple files, and more.
 
 The file is named `dart_test.yaml` and lives at the root of the package, next to
 the package's pubspec. Like the pubspec, it's a [YAML][] file. Here's an
 example:
 
 [YAML]: http://yaml.org/
 
@@ skipping 17 matching lines @@
   * [`timeout`](#timeout)
   * [`verbose_trace`](#verbose_trace)
   * [`js_trace`](#js_trace)
   * [`skip`](#skip)
   * [`test_on`](#test_on)
 * [Runner Configuration](#runner-configuration)
   * [`paths`](#paths)
   * [`filename`](#filename)
   * [`names`](#names)
   * [`plain_names`](#plain_names)
+  * [`include_tags`](#include_tags)
+  * [`exclude_tags`](#exclude_tags)
   * [`platforms`](#platforms)
   * [`concurrency`](#concurrency)
   * [`pub_serve`](#pub_serve)
   * [`reporter`](#reporter)
 * [Configuring Tags](#configuring-tags)
   * [`tags`](#tags)
   * [`add_tags`](#add_tags)
 * [Configuring Platforms](#configuring-platforms)
   * [`on_os`](#on_os)
   * [`on_platform`](#on_platform)
@@ skipping 130 matching lines @@
 to `"*_test.dart"`.
 
 ```yaml
 filename: "test_*.dart"
 ```
 
 [glob syntax]: https://github.com/dart-lang/glob#syntax
 
 ### `names`
 
-This field restricts the tests run by the runner to those whose names match the
-given regular expressions. A test's name must match *all* regular expressions in
+This field causes the runner to only run tests whose names match the given
+regular expressions. A test's name must match *all* regular expressions in
 `names`, as well as containing all strings in [`plain_names`](#plain_names), in
 order to be run.
 
 This is usually used in a [preset](#configuration-presets) to make it possible
 to quickly select a given set of tests.
 
 ```yaml
 presets:
   # Pass "-P chrome" to run only Chrome tests.
   chrome:
     names:
     - "^browser:"
     - "[Cc]hrome"
 ```
 
 ### `plain_names`
 
-This field restricts the tests run by the runner to those whose names contain
-the given strings. A test's name must contain *all* strings in `plain_names`, as
-well as matching all regular expressions in [`names`](#names), in order to be
-run.
+This field causes the runner to only run tests whose names contain the given
+strings. A test's name must contain *all* strings in `plain_names`, as well as
+matching all regular expressions in [`names`](#names), in order to be run.
 
 This is usually used in a [preset](#configuration-presets) to make it possible
 to quickly select a given set of tests.
 
 ```yaml
 presets:
   # Pass "-P ie" to run only Internet Explorer tests.
   ie:
     plain_names:
     - "IE"
     - "Internet Explorer"
 ```
 
+### `include_tags`
+
+This field causes the runner to only run tests whose tags match the given
+[boolean selector][]. If both `include_tags` and [`exclude_tags`](#exclude_tags)
+are used, the exclusions take precedence.
+
+[boolean selector]: https://github.com/dart-lang/boolean_selector/blob/master/README.md
+
+This is usually used in a [preset](#configuration-preset) to make it possible to
+quickly select a set of tests.
+
+```yaml
+presets:
+  # Pass "-P windowless" to run tests that don't open browser windows.
+  windowless:
+    include_tags: !browser || content-shell
+```
+
+### `exclude_tags`
+
+This field causes the runner not to run tests whose tags match the given
+[boolean selector][]. If both [`include_tags`](#include_tags) and `exclude_tags`
+are used, the exclusions take precedence.
+
+This is usually used in a [preset](#configuration-preset) to make it possible to
+quickly select a set of tests.
+
+```yaml
+presets:
+  # Pass "-P windowless" to run tests that don't open browser windows.
+  windowless:
+    exclude_tags: browser && !content-shell
+```
+
 ### `platforms`
 
 This field indicates which platforms tests should run on by default. It allows
 the same platform identifiers that can be passed to `--platform`. If multiple
 platforms are included, the test runner will default to running tests on all of
 them. This defaults to `[vm]`.
 
 ```yaml
 platforms: [content_shell]
 
@@ skipping 234 matching lines @@
 presets:
   # Shortcut for running only browser tests.
   browser:
     paths: [test/runner/browser]
 
   # Shortcut for running only Chrome tests.
   chrome:
     filename: "chrome_*_test.dart"
     add_presets: [browser]
 ```