Clean up core.gyp.

Since core.gyp uses both includes and excludes rule, it is a little dirty and difficult to read.
Instead, we should explicitly exclude platform-specific files from one global file list.

BUG=358074

Review URL: https://codereview.chromium.org/890023004

git-svn-id: svn://svn.chromium.org/blink/trunk@189773 bbb929c8-8fbe-4397-9dbb-9b2b20218538
4 files changed