[sebxt]

SourceMapConsumer.fromSourceMap accepts a sourceMapUrl argument (see the JSDoc and source-map.d.ts), but BasicSourceMapConsumer.fromSourceMap did not forward it to the constructor. As a result relative sources were not resolved against the map's URL, unlike new SourceMapConsumer(map, url).

This forwards the URL to the constructor.

Testing: added test SourceMapConsumer.fromSourceMap with a source map URL in test/test-source-map-consumer.js, which checks sources, originalPositionFor and sourceContentFor against the resolved URL. It fails on current master ('src/a.js' == 'http://example.com/maps/src/a.js') and passes with the fix. npm test passes (191 / 191), and eslint and prettier are clean on the touched files.

Fixes #544