GN: fix bootstrap
GN: fix bootstrap

//base/trace_event/memory_dump_manager.cc now needs the generated
//base/debug/debugging_flags.h file.

Generating that file when building manually with ninja fixes
bootstrapping.

R=brettw@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/1929403002
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#391055}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk