[Cast Convergence] Replace is_cast_desktop_build with is_castos.

This patch moves is_cast_desktop_build to //chromecast and replaces
usages with a new flag, is_castos, which guards code intended for
Nest Linux devices.

The flag defaults to is_chromecast for now; in the future it will be
default to false, and individual builds will need to opt into building
Nest Linux specific code.

Bug: 1293569
Change-Id: Ib4075f415a59048c787b02c8532e2e0a20abfaff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3606171
Reviewed-by: Will Cassella <cassew@chromium.org>
Reviewed-by: Mark Foltz <mfoltz@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Reviewed-by: Peter Wen <wnwen@chromium.org>
Commit-Queue: Ryan Keane <rwkeane@google.com>
Reviewed-by: Sean Topping <seantopping@chromium.org>
Cr-Commit-Position: refs/heads/main@{#998482}
NOKEYCHECK=True
GitOrigin-RevId: af3ac0f74f1fb633db1b4b4239ad9756237459d6

BUILD.gn

@@ -31,7 +31,10 @@ buildflag_header("branding_buildflags") {
 buildflag_header("chromecast_buildflags") {
   header = "chromecast_buildflags.h"
 
-  flags = [ "IS_CHROMECAST=$is_chromecast" ]
+  flags = [
+    "IS_CHROMECAST=$is_chromecast",
+    "IS_CASTOS=$is_castos",
+  ]
 }
 
 buildflag_header("chromeos_buildflags") {

config/chromecast_build.gni

@@ -34,32 +34,28 @@ declare_args() {
 
   # True to enable the cast audio renderer.
   #
-  # TODO(crbug.com/1293520):  Remove this buildflag.
+  # TODO(crbug.com/1293520): Remove this buildflag.
   enable_cast_audio_renderer = false
 }
 
 declare_args() {
   # Set this true for a Chromecast build. Chromecast builds are supported on
-  # Linux and Android.
+  # Linux, Android, ChromeOS, and Fuchsia.
   #
   # During the migration from is_chromecast, this must be set to the same value
   # as is_chromecast.
   enable_cast_receiver = is_chromecast
-}
 
-declare_args() {
-  # True if Chromecast build is targeted for linux desktop. This type of build
-  # is useful for testing and development, but currently supports only a subset
-  # of Cast functionality. Though this defaults to true for x86 Linux devices,
-  # this should be overriden manually for an embedded x86 build.
-  # TODO(slan): Remove instances of this when x86 is a fully supported platform.
+  # Set this to true to build for Nest hardware running Linux (aka "CastOS").
+  # Set this to false to use the defaults for the target OS/platform.
   #
-  # TODO(crbug.com/1293569): Move is_cast_desktop_build to //chromecast.
-  is_cast_desktop_build = enable_cast_receiver && target_os == "linux" &&
-                          (target_cpu == "x86" || target_cpu == "x64")
+  # TODO(crbug.com/1314528): Change default to false and require is_linux.
+  is_castos = is_chromecast
+}
 
-  # True to enable the cast renderer.  It is enabled by default for linux and
-  # android audio only builds.
+declare_args() {
+  # True to enable the cast renderer.  It is enabled by default for Linux and
+  # Android audio only builds.
   #
   # TODO(crbug.com/1293520):  Remove this buildflag.
   enable_cast_renderer =
@@ -124,12 +120,11 @@ assert(is_linux || is_chromeos || is_android || is_fuchsia ||
            !enable_cast_receiver,
        "Cast receiver builds are not supported on $target_os")
 
-# Assert that is_cast_audio_only and is_cast_desktop_build are both false on a
-# non-Chromecast build.
-#
-# NOTE: This restriction should be removed in the future as it should be
-# possible to build an audio-only Cast-enabled browser on any platform.
-assert(enable_cast_receiver || (!is_cast_audio_only && !is_cast_desktop_build))
+assert(enable_cast_receiver || !is_cast_audio_only,
+       "is_cast_audio_only = true requires enable_cast_receiver = true.")
 
 assert(enable_cast_receiver == is_chromecast,
        "enable_cast_receiver and is_chromecast must be set to the same value.")
+
+assert(enable_cast_receiver || !is_castos,
+       "is_castos = true requires enable_cast_receiver = true.")

config/ozone.gni

@@ -10,7 +10,7 @@ declare_args() {
   # Indicates if Ozone is enabled. Ozone is a low-level library layer for Linux
   # that does not require X11.
   use_ozone =
-      is_chromeos || (is_chromecast && !is_android) || is_fuchsia || is_linux
+      is_chromeos || (is_castos && !is_android) || is_fuchsia || is_linux
 }
 
 declare_args() {
@@ -71,15 +71,15 @@ declare_args() {
 
     if (is_cast_audio_only) {
       # Just use headless for audio-only Cast platforms.
-    } else if (is_chromecast && !is_fuchsia) {
-      # Enable the Cast ozone platform on all A/V Cast builds except Fuchsia.
+    } else if (is_castos && !is_fuchsia) {
+      # Enable the Cast ozone platform on all video CastOS builds.
       ozone_platform_cast = true
 
       # For visual desktop Chromecast builds, override the default "headless"
       # platform with --ozone-platform=x11.
-      # TODO(halliwell): Create a libcast_graphics implementation for desktop
-      # using X11, and disable this platform.
-      if (is_cast_desktop_build && !is_cast_audio_only) {
+      # NOTE: The CQ is one such case.
+      if (target_os == "linux" &&
+          (target_cpu == "x86" || target_cpu == "x64")) {
         ozone_platform_x11 = true
       } else {
         ozone_platform = "cast"