Allow configuration of JVM arguments in build

tasks/readme.md

@@ -13,12 +13,18 @@ Builds the library based on a configuration file.  See the `--help` option for m
 
 Build configuration files are JSON files that are used to determine what should be exported from the library and what options should be passed to the compiler.
 
+**Required configuration properties**
+
  * **exports** - `Array.<string>` An array of symbol names or patterns to be exported (names that are used in your application).  For example, including `"ol.Map"` will export the map constructor.  Method names are prefixed with `#`.  So `"ol.Map#getView"` will export the map's `getView` method.  You can use a `*` at the end to match multiple names.  The pattern `"ol.Map#*"` will export all map methods.
 
  * **compile** - `Object` An object whose properties are [Closure Compiler options](https://github.com/openlayers/closure-util/blob/master/compiler-options.txt).  Property names match the option names without the `--` prefix (e.g. `"compilation_level": "ADVANCED_OPTIMIZATIONS"` would set the `--compilation_level` option).  Where an option can be specified multiple times, use an array for the value (e.g. `"externs": ["one.js", "two.js"]`).  Where an option is used as a flag, use a boolean value (e.g. `"use_types_for_optimization": true`).
 
+**Optional configuration properties**
+
  * **src** - `Array.<string>` Optional array of [path patterns](https://github.com/isaacs/minimatch/blob/master/README.md) for source files.  This defaults to `["src/**/*.js"]` which will match all `.js` files in the `src` directory.  To include a different set of source files, provide an array of path patterns.  Note that these patterns are `/` delimited even on Windows.
 
+ * **jvm** - `Array.<string>` Optional array of [command line options](https://code.google.com/p/closure-compiler/wiki/FAQ#What_are_the_recommended_Java_VM_command-line_options?) for the compiler.  By default, the Compiler is run with `['-server', '-XX:+TieredCompilation']`.
+
 The build task generates a list of source files sorted in dependency order and passes these to the compiler.  This takes the place of the `--js` options that you would use when calling the compiler directly.  If you want to add additional source files, typically you would use the `src` array described above.  This works with sources that have `goog.require` and/or `goog.provide` calls (which are used to sort dependencies).  If you want to force the inclusion of files that don't use `goog.require` or `goog.provide`, you can use the `js` property of the `compile` object.  Paths in the `js` array will be passed to the compiler **after** all other source files.
 
 Paths in your config file should be relative to the current working directory (when you call `node tasks/build.js`).  Note that this means paths are not necessarily relative to the config file itself.