Add support for overriding keystore for signing.

build/config/android/config.gni

 # 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.
 
 # This file contains common system config stuff for the Android build.
 
 if (is_android) {
   has_chrome_android_internal =
       exec_script("//build/dir_exists.py",
                   [ rebase_path("//clank", root_build_dir) ],
                   "string") == "True"
 
   if (has_chrome_android_internal) {
     import("//clank/config.gni")
   }
 
   if (!defined(default_android_sdk_root)) {
     default_android_sdk_root = "//third_party/android_tools/sdk"
     default_android_sdk_version = "23"
     default_android_sdk_build_tools_version = "23.0.0"
   }
 
+  if (!defined(default_android_keystore_path)) {
+    default_android_keystore_path =
+        "//build/android/ant/chromium-debug.keystore"
+    default_android_keystore_name = "chromiumdebugkey"
+    default_android_keystore_password = "chromium"
+  }
+
   if (!defined(google_play_services_library)) {
     google_play_services_library =
         "//third_party/android_tools:google_play_services_default_java"
   }
 
   if (!defined(google_play_services_resources)) {
     google_play_services_resources =
         "//third_party/android_tools:google_play_services_default_resources"
   }
 
   declare_args() {
     android_sdk_root = default_android_sdk_root
     android_sdk_version = default_android_sdk_version
     android_sdk_build_tools_version = default_android_sdk_build_tools_version
 
-    android_default_keystore_path =
-        "//build/android/ant/chromium-debug.keystore"
-    android_default_keystore_name = "chromiumdebugkey"
-    android_default_keystore_password = "chromium"
+    # The path to the keystore to use for signing builds.
+    android_keystore_path = default_android_keystore_path
+
+    # The name of the keystore to use for signing builds.
+    android_keystore_name = default_android_keystore_name
+
+    # The password for the keystore to use for signing builds.
+    android_keystore_password = default_android_keystore_password
 
     # This is a unique identifier for a given build. It's used for
     # identifying various build artifacts corresponding to a particular build of
     # chrome (e.g. where to find archived symbols).
     android_chrome_build_id = "\"\""
 
     # Set to true to run findbugs on JAR targets.
     run_findbugs = false
 
     # Set to true to enable verbose findbugs logging. This does nothing if
@@ skipping 144 matching lines @@
   } else if (current_cpu == "x64") {
     android_app_abi = "x86_64"
   } else if (current_cpu == "arm64") {
     android_app_abi = "arm64-v8a"
   } else if (current_cpu == "mips64el") {
     android_app_abi = "mips64"
   } else {
     assert(false, "Unknown Android ABI: " + current_cpu)
   }
 }