Improve public header file checking

tools/gn/variables.cc

Index: tools/gn/variables.cc
diff --git a/tools/gn/variables.cc b/tools/gn/variables.cc
index 8e41e62cbe5ff40aae006202f931939ab42ac022..4b49f60b30f3d7d334c9e05045612a91556197d5 100644
--- a/tools/gn/variables.cc
+++ b/tools/gn/variables.cc
@@ -684,36 +684,32 @@ const char kPublic_HelpShort[] =
 const char kPublic_Help[] =
     "public: Declare public header files for a target.\n"
     "\n"
-    "  A list of files and patterns that other targets can include. These\n"
-    "  permissions are checked via the \"check\" command\n"
-    "  (see \"gn help check\").\n"
+    "  A list of files that other targets can include. These permissions are\n"
+    "  checked via the \"check\" command (see \"gn help check\").\n"
     "\n"
     "  If no public files are declared, other targets (assuming they have\n"
-    "  visibility to depend on this target) can include any file. If this\n"
-    "  variable is defined on a target, dependent targets may only include\n"
-    "  files on this whitelist.\n"
-    "\n"
-    "  The entries in this list are patterns (see \"gn help patterns\") so\n"
-    "  you can use simple wildcard matching if you have a directory of public\n"
-    "  files.\n"
+    "  visibility to depend on this target can include any file in the\n"
+    "  sources list. If this variable is defined on a target, dependent\n"
+    "  targets may only include files on this whitelist.\n"
     "\n"
     "  Header file permissions are also subject to visibility. A target\n"
     "  must be visible to another target to include any files from it at all\n"
     "  and the public headers indicate which subset of those files are\n"
-    "  permitted.\n"
+    "  permitted. See \"gn help visibility\" for more.\n"
     "\n"
     "  Public files are inherited through the dependency tree. So if there is\n"
     "  a dependency A -> B -> C, then A can include C's public headers.\n"
     "  However, the same is NOT true of visibility, so unless A is in C's\n"
     "  visibility list, the include will be rejected.\n"
     "\n"
+    "  GN only knows about files declared in the \"sources\" and \"public\"\n"
+    "  sections of targets. If a file is included that is now known to the\n"
+    "  build, it will be allowed.\n"
+    "\n"
     "Examples:\n"
     "  These exact files are public:\n"
     "    public = [ \"foo.h\", \"bar.h\" ]\n"
     "\n"
-    "  All files in the \"public\" directory are public:\n"
-    "    public = [ \"public/*\" ]\n"
-    "\n"
     "  No files are public (no targets may include headers from this one):\n"
     "    public = []\n";