Remove obsolete GN check.md documentation.

tools/gn/docs/check.md

Index: tools/gn/docs/check.md
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-# GN Check
-
-GN has several different ways to check dependencies. Many of them are checked by
-the `gn check` command. Running checks involve opening and scanning all source
-files so this isn't run every time a build is updated. To run check on an
-existing build:
-
-    gn check out/mybuild
-
-To run the check as part of the "gen" command to update the build (this is what
-the bots do):
-
-    gn gen out/mybuild --check
-
-[TOC]
-
-## Concepts
-
-### Visibility
-
-Targets can control which other targets may depend on them by specifying
-`visibility`. Visibility is always checked when running any GN command (not just
-`gn check`.
-
-By default, targets are "public" meaning any target can depend on them. If you
-supply a list, visibility will be listed to those targets (possibly including
-wildcards):
-
-```
-visibility = [
-  ":*",  # All targets in this file.
-  "//content/*",  # All targets in content and any subdirectory thereof.
-  "//tools:doom_melon",  # This specific target.
-]
-```
-
-See `gn help visibility` for more details and examples.
-
-### Public header files
-
-Targets can control which headers may be included by dependent targets so as to
-define a public API. If your target specifies only `sources`, then all headers
-listed there are public and can be included by all dependents.
-
-If your target defines a `public` variable, only the files listed in that list
-will be public. Files in `sources` but not `public` (they can be in both or only
-one) may not be included by dependent targets.
-
-```
-source_set("foo") {
-  public = [
-    "foo.h",
-    "foo_config.h",
-  ]
-  sources = [
-    "foo.cc",
-    "foo.h",
-    "bar.cc",
-    "bar.h",
-  ]
-}
-```
-
-### Public dependencies
-
-In order to include files from your target, that target must be listed in your
-target's dependencies. By default, transitively depending on a target doesn't
-give your files this privilege.
-
-If a target exposes a dependency as part of its public API, then it can list
-that dependency as a `public_deps`:
-
-```
-source_set("foo") {
-  sources = [ ... ]
-  public_deps = [
-    "//base",
-  ]
-  deps = [
-    "//tools/doom_melon",
-  ]
-}
-```
-
-Targets that depend on `foo` can include files from `base` but not from
-`doom_melon`. To include public headers from `doom\_melon, a target would need
-to depend directly on it.
-
-Public dependencies work transitively, so listing a target as a public
-dependency also exposes that target's public dependencies. Along with the
-ability to include headers, public dependencies forward the `public_configs`
-which allow settings like defines and include directories to apply to
-dependents.
-
-## Putting it all together
-
-In order to include a header from target Y in a file that is part of target X:
-
-*   X must be in Y's `visibility` list (or B must have no `visibility` defined).
-*   The header must be in Y's `public` headers (or Y must have no `public`
-    variable defined).
-*   X must depend directly on Y, or there must be a path from X to Y following
-    only public dependencies.
-
-### What gets checked
-
-Chrome currently doesn't come close to passing a `gn check` pass. You can check
-specific targets or subtrees for issues:
-
-    gn check out/mybuild //base
-
-    gn check out/mybuild "//mojo/*"