Add missing MSVS project XML file paths to .gitignore.

Add missing MSVS project XML file paths to .gitignore.

As of #298318, "git status" reports these untracked files.
(GYP generates these for MSVS project schema definitions)
Add the file paths to .gitignore, like others, for sanity.

I found the following .xml entries with no associated GYP target:
  /chrome/tab_capture_performance_tests_run.xml
    (legit: tools/build/scripts/master/factory/chromium_commands.py)
  /ppapi/native_client/src/shared/ppapi_proxy/nacl_ppapi_browser.xml
    (seems stale, but gab added in r126724 for building all.sln)
  /ppapi/native_client/src/shared/ppapi_proxy/ppruntime_lib.xml
    (seems stale, but gab added in r126724 for building all.sln)
  /remoting/proto/trace_proto_lib.xml
    (seems stale, but referenced in tools/emacs/trybot-mac.txt)
  /remoting/remoting_host_installation_unittest.xml
    (seems stale, no other mention; alexeypa added in r135217)
  /tools/metrics/histograms/histograms.before.pretty-print.xml
    (legit: tools/metrics/histograms/pretty_print.py)
I removed the entries for the middle four apparently stale paths.

BUG=NONE
TEST=Cleaner "git status" on Windows machines.
R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/637643002

Cr-Commit-Position: refs/heads/master@{#298578}