1244931 - Create a RAII class for side stepping error reporting.

Status: RESOLVED INCOMPLETE

(Core :: JavaScript Engine, defect)

Description

[Morgan Phillips [:mrrrgn]]

JS_SetErrorReporter returns  a copy of the old error reporter which encourages the following pattern:

JSErrorReporter older = JS_SetErrorReporter(cx->runtime(), nullptr);
// ... some sneaky things with no error reporting
JS_SetErrorReporter(cx->runtime(), older);

What happens when we forget to reset the old error reporter? This is a foot gun. Let's survey where this happens and fix them up with an RAII style class.