Add conditional variable to control boringssl dependency checkout

Change-Id: Ic568070abf783b6089a175ddcec3e3bca68838bb
diff --git a/DEPS b/DEPS
index a4beedc..cbc16a2 100644
--- a/DEPS
+++ b/DEPS
@@ -3,6 +3,8 @@
 vars = {
   'boringssl_git': 'https://boringssl.googlesource.com',
   'chromium_git': 'https://chromium.googlesource.com',
+
+  'checkout_chromium_quic_boringssl': True,
 }
 
 deps = {
@@ -10,7 +12,9 @@
     Var('chromium_git') + '/chromium/src/base' + '@' +
     '6abc23a6273fa803f6f633ad0c77358998db0489',
 
-  'third_party/boringssl/src':
-    Var('boringssl_git') + '/boringssl.git' + '@' +
+  'third_party/boringssl/src': {
+    'url': Var('boringssl_git') + '/boringssl.git' + '@' +
     '6410e18e9190b6b0c71955119fbf3cae1b9eedb7',
+    'condition': 'checkout_chromium_quic_boringssl',
+  }
 }
diff --git a/third_party/BUILD.gn b/third_party/BUILD.gn
index 27cc3a3..359e677 100644
--- a/third_party/BUILD.gn
+++ b/third_party/BUILD.gn
@@ -15,7 +15,6 @@
 
   deps = [
     ":quic_trace",
-    "boringssl",
     "icu:icuuc",
     "protobuf:protobuf_full",
     "zlib",