Adding macro to enable changing SSL library (Part 1)

This changes the macro used to be USE_NSS_VERIFIER and modifies build
files to no longer assume iOS is using NSS.

BUG=591545

Review URL: https://codereview.chromium.org/1808963004

Cr-Original-Commit-Position: refs/heads/master@{#382077}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: a1714ab3703201b3a3c424fa42788f0e4d060b26
diff --git a/tools/gn/docs/cookbook.md b/tools/gn/docs/cookbook.md
index 3fa16e2..febc16c 100644
--- a/tools/gn/docs/cookbook.md
+++ b/tools/gn/docs/cookbook.md
@@ -279,6 +279,7 @@
 | `use_gnome_keyring` (0/1)               | `is_desktop_linux` (true/false)                |                               |
 | `use_goma` (0/1)                        | `use_goma` (true/false)                        | `//build/toolchain/goma.gni`  |
 | `use_nss_certs` (0/1)                   | `use_nss_certs` (true/false)                   | `//build/config/crypto.gni` (Many of these conditions can be deleted, see the "SSL" notes on targets below.) |
+| `use_nss_verifier` (0/1)                | `use_nss_verifier` (true/false)                | `//build/config/crypto.gni` (Many of these conditions can be deleted, see the "SSL" notes on targets below.) |
 | `use_openssl` (0/1)                     | `use_openssl` (true/false)                     | `//build/config/crypto.gni` (Many of these conditions can be deleted, see the "SSL" notes on targets below.) |
 | `use_pango` (0/1)                       | `use_pango` (true/false)                       | `//build/config/ui.gni`       |
 | `use_ozone` (0/1)                       | `use_ozone` (true/false)                       | `//build/config/ui.gni`       |