[Chromecast] Replace architecure-based conditionals with flag.

ui/ozone/ozone.gni

Index: ui/ozone/ozone.gni
diff --git a/ui/ozone/ozone.gni b/ui/ozone/ozone.gni
index 05994bd5689c356536e7c522bc52f37f8747868b..3284f330c2954c0f3b02114fe7c45ab68aee97ef 100644
--- a/ui/ozone/ozone.gni
+++ b/ui/ozone/ozone.gni
@@ -36,12 +36,15 @@ declare_args() {
     if (is_chromecast) {
       if (!disable_display) {
         # Enable the Cast ozone platform on all A/V Cast builds.
+        # TODO(slan|halliwell): Make the default platform "cast" on desktop too.
         ozone_platform_cast = true
 
         # For desktop Chromecast builds, override the default "headless"
         # platform with --ozone-platform=egltest
-        # TODO(slan|halliwell): Make the default platform "cast" on desktop too.
-        if (target_os == "linux" && target_cpu != "arm") {
+        # TODO(tsunghung): When we have a functioning software-decode CMA
+        # implementation, remove this condition - we want to be using the "cast"
+        # platform on every A/V build.

[halliwell, 2015/12/15 02:18:46]

I don't think this has anything to do with CMA.  The TODO here is to create a
cast vendor graphics shared lib implementation for desktop that uses x11.  And
can leave my name against it.

[slan, 2015/12/15 03:11:11]

Right you are, TODO updated and reassigned.

+        if (is_cast_desktop_build) {
           ozone_platform_egltest = true
           ozone_platform_ozonex = true
         } else {