Prepare SourceMapNamesResolver.js for source map asyncification
Prepare SourceMapNamesResolver.js for source map asyncification

This CL prepares {SourceMapNamesResolver._resolveExpression} for the
upcoming asyncification of
{DebuggerWorkspaceBinding.uiLocationToRawLocations}.

R=8abd9e3d93041d096604cb2a1b3070dd7075ba7b@chromium.org

Bug: chromium:1032016
Change-Id: Iebe22450bcf7f87073b783e2f1d679c98e25f17b
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/1994961
Commit-Queue: Simon Zünd <38944668e9e2ca98ccd0275b53370f90fa55c113@chromium.org>
Reviewed-by: Jan Scheffler <8abd9e3d93041d096604cb2a1b3070dd7075ba7b@chromium.org>

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