Exports the compiler metrics gathered by the precompile and
compilePermutation steps into an XML file to be read by external tools.
See compilerMetrics.xsd for an XML schema describing the output.
<metrics version="1">
<module elapsed="1234">
<sources count="1">
<source name="foo.java" />
</sources>
<types count="1" kind="initial">
<type name="com.google.foo.Foo" />
</types>
</module>
<precompilations>
<precompilation base="0" ids="0,1,2" elapsed="1">
<types count="1" kind="generated">
<type name="com.google.foo.Bar" />
</types>
<types count="2" kind="ast">
<type name="com.google.foo.Foo" />
<type name="com.google.foo.Bar" />
</types>
</precompilation>
</precompilations>
<compilations>
<compilation id="0" elapsed="1" totalElapsed="2" description="foo">
<javascript fragments="1" size="123">
<fragment size="123" initial="true" />
</javascript>
</compilation>
</compilations>
</metrics>