Build third_party/zlib/google only when build_with_chromium is true.

This lets other projects reuse the plain parts of third_party/zlib
without depending on Chromium's base/.

BUG=541704

Review-Url: https://codereview.chromium.org/2781353002
Cr-Original-Commit-Position: refs/heads/master@{#460863}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: da0685cc8b20ccce91494583f91aa4a8723ad7c3

BUILD.gn

@@ -2,6 +2,8 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build_overrides/build.gni")
+
 config("zlib_config") {
   include_dirs = [ "." ]
 }
@@ -135,27 +137,29 @@ static_library("minizip") {
   public_configs = [ ":zlib_config" ]
 }
 
-static_library("zip") {
-  sources = [
-    "google/zip.cc",
-    "google/zip.h",
-    "google/zip_internal.cc",
-    "google/zip_internal.h",
-    "google/zip_reader.cc",
-    "google/zip_reader.h",
-  ]
-  deps = [
-    ":minizip",
-    "//base",
-  ]
-}
+if (build_with_chromium) {
+  static_library("zip") {
+    sources = [
+      "google/zip.cc",
+      "google/zip.h",
+      "google/zip_internal.cc",
+      "google/zip_internal.h",
+      "google/zip_reader.cc",
+      "google/zip_reader.h",
+    ]
+    deps = [
+      ":minizip",
+      "//base",
+    ]
+  }
 
-static_library("compression_utils") {
-  sources = [
-    "google/compression_utils.cc",
-    "google/compression_utils.h",
-  ]
-  deps = [
-    ":zlib",
-  ]
+  static_library("compression_utils") {
+    sources = [
+      "google/compression_utils.cc",
+      "google/compression_utils.h",
+    ]
+    deps = [
+      ":zlib",
+    ]
+  }
 }