[gn] Set reasonable defaults for debugging

BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/dcheck_always_on.gni")
 import("//build/config/mips.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
@@ skipping 34 matching lines @@
   v8_enable_i18n_support = true
 
   # Enable slow dchecks.
   v8_enable_slow_dchecks = false
 
   # Interpreted regexp engine exists as platform-independent alternative
   # based where the regular expression is compiled to a bytecode.
   v8_interpreted_regexp = false
 
   # Sets -dOBJECT_PRINT.
-  v8_object_print = false
+  v8_object_print = ""
 
   # With post mortem support enabled, metadata is embedded into libv8 that
   # describes various parameters of the VM for use by debuggers. See
   # tools/gen-postmortem-metadata.py for details.
   v8_postmortem_support = false
 
   # Similar to vfp but on MIPS.
   v8_can_use_fpu_instructions = true
 
   # Similar to the ARM hard float ABI but on MIPS.
@@ skipping 10 matching lines @@
   }
 }
 if (v8_enable_gdbjit == "") {
   if (defined(v8_enable_gdbjit_default)) {
     v8_enable_gdbjit = v8_enable_gdbjit_default
   } else {
     v8_enable_gdbjit = false
   }
 }
 
+# Derived defaults.
+if (v8_object_print == "") {
+  v8_object_print = is_debug && !v8_optimized_debug

[Yang, 2016/07/26 09:01:20]

also set v8_enable_disassembler please

+}
+
 v8_generated_peephole_source = "$target_gen_dir/bytecode-peephole-table.cc"
 v8_random_seed = "314159265"
 v8_toolset_for_shell = "host"
 
 ###############################################################################
 # Configurations
 #
 config("internal_config") {
   visibility = [ ":*" ]  # Only targets in this file can depend on this.
 
@@ skipping 2415 matching lines @@
 
   deps = [
     ":fuzzer_support",
   ]
 
   configs = [ ":internal_config" ]
 }
 
 v8_fuzzer("wasm_asmjs_fuzzer") {
 }