Add defer-layout tool.

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,
@@ skipping 55 matching lines @@
 
   * [`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.
-    
+
   * [`deferred_library_size`][deferred_size]: a tool that gives a breakdown of
     the sizes of the deferred parts of the program. This can show how much of
     your total code size can be loaded deferred.
 
+  * [`deferred_library_layout`][deferred_layout]: a tool that reports which
+    code is included on each output unit.
+
   * [`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
@@ skipping 172 matching lines @@
 ------------------------------------------------
 main                                    12345678
 foo                                      7654321
 bar                                      1234567
 ------------------------------------------------
 Main chunk size                         12345678
 Deferred code size                       8888888
 Percent of code deferred                  41.86%
 ```
 
+### Deferred library layout tool
+
+This tool reports which code is included in each output unit.  It can be run as
+follows:
+
+```bash
+pub global activate dart2js_info # only needed once
+dart2js_info_deferred_library_layout out.js.info.json
+```
+
+The tool will output a table listing all of the deferred output units or chunks,
+for each unit it will list the set of libraries that contribute code to this
+unit. If a library contributes to more than one output unit, the tool lists
+which elements are in one or another output unit. For example, the output might
+look like this:
+
+```
+Output unit main:
+  loaded by default
+  contains:
+     - hello_world.dart
+     - dart:core
+     ...
+
+Output unit 2:
+  loaded by importing: [b]
+  contains:
+     - c.dart:
+       - function d
+     - b.dart
+
+Output unit 1:
+  loaded by importing: [a]
+  contains:
+     - c.dart:
+       - function c
+     - a.dart
+```
+
+In this example, all the code of `b.dart` after tree-shaking was included in the
+output unit 2, but `c.dart` was split between output unit 1 and output unit 2.
+
 ### 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
@@ skipping 62 matching lines @@
 
 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
 [deferred_lib]: https://github.com/dart-lang/dart2js_info/blob/master/bin/deferred_library_check.dart
 [deferred_size]: https://github.com/dart-lang/dart2js_info/blob/master/bin/deferred_library_size.dart
+[deferred_layout]: https://github.com/dart-lang/dart2js_info/blob/master/bin/deferred_library_layout.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