Exclude Observatory assets from PRODUCT build dart, dart_precompiled_runtime

build/config/BUILDCONFIG.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # =============================================================================
 # PLATFORM SELECTION
 # =============================================================================
 #
 # There are two main things to set: "os" and "cpu". The "toolchain" is the name
 # of the GN thing that encodes combinations of these things.
@@ skipping 218 matching lines @@
   _native_compiler_configs += [
     "//build/config/win:lean_and_mean",
     "//build/config/win:nominmax",
     "//build/config/win:sdk",
     "//build/config/win:unicode",
     "//build/config/win:winver",
   ]
 }
 if (is_posix) {
   _native_compiler_configs += [ "//build/config/gcc:no_exceptions" ]
+  if (is_product) {
+    _native_compiler_configs +=
+        [ "//build/config/gcc:symbol_visibility_hidden" ]
+  }
 }
 
 if (is_linux) {
   _native_compiler_configs += [ "//build/config/linux:sdk" ]
 } else if (is_mac) {
   _native_compiler_configs += [ "//build/config/mac:sdk" ]
 } else if (is_android) {
   _native_compiler_configs += [ "//build/config/android:sdk" ]
 }
 
@@ skipping 214 matching lines @@
       sources = invoker.sources
     }
     if (defined(invoker.testonly)) {
       testonly = invoker.testonly
     }
     if (defined(invoker.visibility)) {
       visibility = invoker.visibility
     }
   }
 }