Build libmonochrome.so with secondary toolchain

chrome/android/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/android/rules.gni")
 import("//build_overrides/v8.gni")
 import("//chrome/android/chrome_public_apk_tmpl.gni")
 import("//chrome/common/features.gni")
 import("//chrome/version.gni")
@@ skipping 436 matching lines @@
   ]
 
   if (is_android && use_order_profiling) {
     deps += [ "//tools/cygprofile" ]
   }
 
   public_configs = extra_chrome_shared_library_configs
 }
 
 # GYP: none
-if (!defined(webview_only_libmonochrome) || !webview_only_libmonochrome) {
+#
+# //chrome/android/monochrome is only needed in two cases

[agrieve, 2016/07/20 02:11:03]

nit: comment says what the if statement says, but doesn't answer the question of
why. It should say why it's needed in only these cases, and why it's worth
putting behind an if()

[michaelbai, 2016/07/20 16:51:11]

Refine the comment, hope it is clear now.

+# - build with 32-bit default_toolchain,
+# - or build with 32-bit android_secondary_abi_toolchain.
+if (!android_64bit_target_cpu ||
+    current_toolchain == android_secondary_abi_toolchain) {
   shared_library("monochrome") {
     sources = chrome_apk_gypi.monochrome_app_native_sources
     deps = [
       "//android_webview:common",
       "//chrome:chrome_android_core",
     ]
 
     configs -= [ "//build/config/android:hide_native_jni_exports" ]
     if (is_android && use_order_profiling) {
       deps += [ "//tools/cygprofile" ]
     }
 
     public_configs = extra_chrome_shared_library_configs
   }
+} else {
+  group("monochrome_secondary_abi_lib") {
+    public_deps = [
+      ":monochrome($android_secondary_abi_toolchain)",
+    ]
+  }
 }
 
 # GYP: //chrome/android/chrome_apk.gyp:libchrome_sync_shell
 shared_library("chrome_sync_shell") {
   testonly = true
   deps = [
     "//build/config/sanitizers:deps",
     "//chrome:chrome_android_core",
     "//sync",
     "//sync:test_support_sync_fake_server_android",
@@ skipping 120 matching lines @@
     apk_name = "ChromeSyncShellTest"
     apk_under_test = ":chrome_sync_shell_apk"
     android_manifest = chrome_sync_shell_test_apk_manifest
     android_manifest_dep = ":chrome_sync_shell_test_apk_manifest"
     deps = [
       ":chrome_sync_shell_test_apk_java",
     ]
     proguard_enabled = !is_java_debug
   }
 }