zlib: moving compression_utils_portable into own GN target

This allows other users of Chromium's zlib library who don't depend on
//base (for example, V8), to reuse some boilerplate code.

Bug: 833361
Change-Id: Ifc9023fdb9915e0452d424b030e8a8e5ae1c0df3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1819838Reviewed-by: Adenilson Cavalcanti <cavalcantii@chromium.org>
Commit-Queue: Adenilson Cavalcanti <cavalcantii@chromium.org>
Commit-Queue: Sam Maier <smaier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699386}

third_party/zlib/google/BUILD.gn

@@ -26,12 +26,23 @@ if (build_with_chromium) {
     sources = [
       "compression_utils.cc",
       "compression_utils.h",
-      "compression_utils_portable.cc",
-      "compression_utils_portable.h",
     ]
     deps = [
+      ":compression_utils_portable",
       "//base",
       "//third_party/zlib",
     ]
   }
 }
+
+# This allows other users of Chromium's zlib library, but don't use Chromium's
+# //base, to reuse some boilerplate code.
+static_library("compression_utils_portable") {
+  sources = [
+    "compression_utils_portable.cc",
+    "compression_utils_portable.h",
+  ]
+  deps = [
+    "//third_party/zlib",
+  ]
+}