Launch bug: https://bugs.chromium.org/p/chromium/issues/detail?id=705916

Add --headless flag to Windows:

Fix browser_tests not compiling properly on windows
Fix headless/BUILD.gn by:
   - Changing headless_lib to a headless component, following steps in https://chromium.googlesource.com/chromium/src/+/master/docs/component_build.md and fixing the build for linux, since it now compiles as a shared_library when component build is true.
   - Adding neccesary HEADLESS_EXPORT (submitted in https://codereview.chromium.org/2775693003/)
   - Disabling breakpad in windows (will fix in a separate CL)

BUG=686608

Review-Url: https://codereview.chromium.org/2762593002
Cr-Commit-Position: refs/heads/master@{#466176}
22 files changed