[Chromecast] Use os_crypt_posix.

    
Chromecast does not set USE_KEYRING, USE_LIBSECRET, or USE_KWALLET, so
there is no benefit os using os_crypt_linux over os_crypt_posix. Use
os_crypt_poxis instead because it does not require setting up an
os_crypt::Config.
    
BUG=750391

Change-Id: Ia320b6c058137d68a55af33bc8ffb9bf5226a325
Reviewed-on: https://chromium-review.googlesource.com/592847Reviewed-by: Christos Froussios <cfroussios@chromium.org>
Commit-Queue: Mike Bjorge <mbjorge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491046}

components/os_crypt/BUILD.gn

@@ -2,6 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/config/chromecast_build.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//build/config/linux/pkg_config.gni")
@@ -69,7 +70,7 @@ static_library("os_crypt") {
     libs = [ "crypt32.lib" ]
   }
 
-  if (is_desktop_linux) {
+  if (is_desktop_linux && !is_chromecast) {
     sources -= [ "os_crypt_posix.cc" ]
     sources += [
       "key_storage_config_linux.cc",