Support more flags in JUnitShell/GWTTestCase

[niloc132]

GWT version: 2.12
Browser (with version): any
Operating System: any

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Description

When testing either an application or non-application project, it can be helpful to be able to tweak GWTTestCases to compile its output in a way that more closely matches how the application itself might run. Specifically, I was surprised to find we couldn't use -strict in tests.

Examples:

• #10037
• -XfragmentCount - super dev mode doesn't support this, which makes sense at this time (see #7711 to consider adding optimization flags to SDM), but it could make sense to allow the same control over split points in tests as we support in the compiler. Note that -XdisableRunAsync is supported for tests.
• -compileReport/-compilerMetrics/-soyc/-XsoycDetailed - apparently only supported for compilation, but I could imagine that this makes sense for some testing or diagnostic purposes. -XdisableSoycHtml/-XenableJsonSoyc could also make sense if we do this?
• -XmethodNameDisplayMode - could make test debugging easier, especially if we can generally disable emulated stack traces and use sourcemaps
• -saveSource/-saveSourceOutput could be useful for some debugging of tests

Steps to reproduce

Pass -strict or -failOnError (or any other flags above) as part of the gwt.args system property when running tests.

Links to further discussions

See also #7711