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Return a Temporary from *Binding::Wrap.

Returning a JS<T> is GC-unsafe.

This commit also includes some cleanup around Node and Document reflection.
Include some jemalloc stats in the -m measurements.
Remove some dead code and fix some pyflakes warnings in CodegenRust.py.
adding 2 new default arguments when running make check-wpt so that it does not fail saying KeyError: 'debug_args' or KeyError: 'interactive'
Update run.py

None and False are better values here (thanks to @jgraham).
Merge pull request #2801 from Ms2ger/wrap-temp

Return a Temporary from *Binding::Wrap.
Merge pull request #2807 from Ms2ger/pyflakes-2

Remove some dead code and fix some pyflakes warnings in CodegenRust.py.
Store proxy handlers in a static array rather than a hashtable per window.
Allow URLSearchParams to be passed to XHR Send()
Merge pull request #2809 from Manishearth/sendparam

Allow URLSearchParams to be passed to XHR Send(); r=jdm
Remove references to WindowProxy as an interface.
Add a test for interfaces exposed on the window object.
Stop exposing XMLHttpRequestEventTarget on the window object.
Merge pull request #2808 from schaars/make_check-wpt

adding 2 default arguments to src/test/wpt/run.py; r=jgraham,Ms2ger
Handle exceptions from JS_ParseJSON in XMLHttpRequest.response.
Merge pull request #2810 from Ms2ger/proxy-handlers

Store proxy handlers in a static array rather than a hashtable per window.
Merge pull request #2813 from Ms2ger/WindowProxy

Remove references to WindowProxy as an interface.
Merge pull request #2815 from Ms2ger/test_interfaces

Add test_interfaces.html.
Merge pull request #2817 from Ms2ger/xhr-response-json

Handle exceptions from JS_ParseJSON in XMLHttpRequest.response.