GN: fix a DCHECK() when generating Visual Studio solution files

VisualStudioWriter::WriteSolutionFileContents() used RebasePath()
with |source_root| = "/" which is forbidden. It always uses system
absolute paths, thus we can use |source_root| = "".

R=brettw@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1723613003

Cr-Original-Commit-Position: refs/heads/master@{#377258}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: bbe9c04f0889293cea85b6806145e26e1670a223
1 file changed
tree: 43604b75e4a9aa597078ddf4dd475514ab75241b
  1. tools/