TaintSpewer

[tmbrbr]

This PR implements #236 by implementing a TaintSpewer.

It uses existing mechanisms to dump large amounts of information to file, namely the StructuredSpewer:

project-foxhound/js/src/util/StructuredSpewer.h

Line 121 in 725e1d9

class StructuredSpewer {

This change adds a new structured SpewChannel, the TaintFlowSpewer, which will then dump a StringTaint object to the SPEW_FILE whenever a sink is hit.

To configure, first build with the following flag in your mozconfig:

ac_add_options --enable-taintspew

And then set the following environment variables:

export SPEW=TaintFlowSpewer,AtStartup
export SPEW_FILE=/path/to/file

The spewer will be disabled by default.

[tmbrbr]

I have also added the foxhound(12345) JavaScript function which implements #237. In this case it prints a message to stderr but also logs it via the TaintSpew channel.

[leeN]

Looks good to me, works as intended based on our testing :)

[leeN]

LGTM