add tool to check that deferred libraries contain the expected code

README.md

 # Dart2js Info
 
 This package contains libraries and tools you can use to process `.info.json`
 files, which are produced when running dart2js with `--dump-info`.
 
 The `.info.json` files contain data about each element included in
 the output of your program. The data includes information such as:
 
   * the size that each function adds to the `.dart.js` output,
   * dependencies between functions,
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   * [`code_deps.dart`][code_deps]: simple tool that can answer queries about the
     dependency between functions and fields in your program. Currently it only
     supports the `some_path` query, which shows a dependency path from one
     function to another.
 
   * [`library_size_split`][lib_split]: a tool that shows how much code was
     attributed to each library. This tool is configurable so it can group data
     in many ways (e.g. to tally together all libraries that belong to a package,
     or all libraries that match certain name pattern).
 
+  * [`deferred_library_check`][deferred_lib]: a tool that verifies that code
+    was split into deferred parts as expected. This tool takes a specification
+    of the expected layout of code into deferred parts, and checks that the
+    output from `dart2js` meets the specification.
+
   * [`function_size_analysis`][function_analysis]: a tool that shows how much
     code was attributed to each function. This tool also uses dependency
     information to compute dominance and reachability data. This information can
     sometimes help determine how much savings could come if the function was not
     included in the program.
 
   * [`coverage_log_server`][coverage] and [`live_code_size_analysis`][live]:
     dart2js has an experimental feature to gather coverage data of your
     application. The `coverage_log_server` can record this data, and
     `live_code_size_analysis` can correlate that with the `.info.json`, so you
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 - regexp: "file:///my/project/dir/(.*)"
 ```
 
 Regardless of the grouping configuration, the tool will display the total code
 size attributed of all libraries, constants, and the program size.
 
 **Note**: eventually you should expect all numbers to add up to the program
 size. Currently dart2js's `--dump-info` is not complete, so numbers for
 bootstrapping code and lazy static initializers are missing.
 
+### Deferred library verification
+
+This tool checks that the output from dart2js meets a given specification,
+given in a YAML file. It can be run as follows:
+
+```bash
+pub global activate dart2js_info # only needed once
+dart2js_info_deferred_library_check out.js.info.json manifest.yaml
+```
+
+The format of the YAML file is:
+
+```yaml
+main:
+  packages:
+    - some_package
+    - other_package
+
+foo:
+  packages:
+    - foo
+    - bar
+
+baz:
+  packages:
+    - baz
+    - quux
+```
+
+The YAML file consists of a list of declarations, one for each deferred
+part expected in the output. At least one of these parts must be named
+"main"; this is the main part that contains the program entrypoint. Each
+top-level part contains a list of package names that are expected to be
+contained in that part. Any package that is not explicitly listed is
+expected to be in the main part. For instance, in the example YAML above
+the part named "baz" is expected to contain the packages "baz" and "quux".
+
+The names for parts given in the specification YAML file (besides "main")
+are arbitrary and just used for reporting when the output does not meet the
+specification.
+
 ### Function size analysis tool
 
 This command-line tool presents how much each function contributes to the total
 code of your application.  We use dependency information to compute dominance
 and reachability data as well.
 
 When you run:
 ```bash
 pub global activate dart2js_info # only needed once
 dart2js_info_function_size_analysis out.js.info.json
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 ## Code location, features and bugs
 
 This package is developed in [github][repo].  Please file feature requests and
 bugs at the [issue tracker][tracker].
 
 [repo]: https://github.com/dart-lang/dart2js_info/
 [tracker]: https://github.com/dart-lang/dart2js_info/issues
 [code_deps]: https://github.com/dart-lang/dart2js_info/blob/master/bin/code_deps.dart
 [lib_split]: https://github.com/dart-lang/dart2js_info/blob/master/bin/library_size_split.dart
+[lib_split]: https://github.com/dart-lang/dart2js_info/blob/master/bin/deferred_library_check.dart
 [coverage]: https://github.com/dart-lang/dart2js_info/blob/master/bin/coverage_log_server.dart
 [live]: https://github.com/dart-lang/dart2js_info/blob/master/bin/live_code_size_analysis.dart
 [function_analysis]: https://github.com/dart-lang/dart2js_info/blob/master/bin/function_size_analysis.dart
 [AllInfo]: http://dart-lang.github.io/dart2js_info/doc/api/dart2js_info.info/AllInfo-class.html