Add informative error messages when parsing command line options returns an error
The background behind why I'm submitting this PR is slightly embarrassing. After running `./mach` with some servo options I got the following stack backtrace.
```
thread '<main>' panicked at 'called `Result::unwrap()` on an `Err` value: ParseIntError { kind: InvalidDigit }', ../src/libcore/result.rs:746
stack backtrace:
1: 0x56459001b0b0 - sys::backtrace::tracing:👿:write::hb120982054a416e35nu
2: 0x56459001e02b - panicking::default_handler::_$u7b$$u7b$closure$u7d$$u7d$::closure.42840
3: 0x56459001dc96 - panicking::default_handler::h7ae2e4523ef4c187IFy
4: 0x56459000760c - sys_common::unwind::begin_unwind_inner::h5fb19481d14902dbDgt
5: 0x564590007cf8 - sys_common::unwind::begin_unwind_fmt::hd62d57279546b0f2Jft
6: 0x56459001a701 - rust_begin_unwind
7: 0x56459004c01f - panicking::panic_fmt::h27f7225e08792f40qYL
8: 0x56458f393901 - result::unwrap_failed::h18215968003310890981
at ../src/libcore/macros.rs:29
9: 0x56458f3937b9 - result::Result<T, E>::unwrap::h10319050269194353824
at ../src/libcore/result.rs:687
10: 0x56458f383701 - opts::from_cmdline_args::h8ea8d8c87dc6ee726lg
at /home/drobertson/git/servo/components/util/opts.rs:599
11: 0x56458d1f8cdf - main::h8517eb49d15e90fbNaa
at /home/drobertson/git/servo/components/servo/main.rs:53
12: 0x56459001d8f4 - sys_common::unwind::try::try_fn::h9076850075504893162
13: 0x56459001a68b - __rust_try
14: 0x56459001d36e - rt::lang_start::h58a22f304b0c1e19Oxy
15: 0x56458d2f4aa9 - main
16: 0x7f370496360f - __libc_start_main
17: 0x56458d1c04a8 - _start
18: 0x0 - <unknown>
Servo exited with return value 101
```
I immediately opened up `gdb` and got to work only to realize that the error was due to a typo in an option that had been `unwrap`ed at [components/util/opts.rs:599](https://github.com/servo/servo/blob/master/components/util/opts.rs#L599). Perhaps some more informative error messages will help prevent some future face-palm moments like mine 😄
I couldn't think of a good way to add tests for this. Please let me know if I missed something. Comments and critiques are welcome!
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Implement Blob response for XMLHttpRequest: #9623
My first attempt at implementing the Blob response for XMLHttpRequest. The expected result for the response `tests/wpt/web-platform-test/HMLHttpRequest/response-blob-data.htm` is also changed to `PASS`. Please let me know if you see any areas in which I can improve this PR!
Fixes#9623
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style: Make the whole style crate independent of the implementation
This allows, among other things, having different implementations for parsing pseudo{elements, classes} in both `ports/geckolib` and in servo.
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This is unfortunate, but making that useful would require parameterizing
`SharedLayoutContext` and `LayoutContext` depending on the
`SelectorImpl` (which is a **huge** work right now).
Probably the easier way to do it, and probably the one that keeps the
layout code more legible, and since there won't be multiple
implementations at the same compilation unit, would be "defining" a
default implementation for layout via feature flags.
That should allow us to remove the components/style/servo.rs file.
This commit refactors the style crate to be completely independent of
the actual implementation and pseudo-elements supported.
This also adds a gecko backend which introduces parsing for the
anonymous box pseudo-elements[1], although there's still no way of
querying them.
https://mxr.mozilla.org/mozilla-central/source/layout/style/nsCSSAnonBoxList.h
