Add is_chromecast to GN build.

chromecast/chromecast.gni

Index: chromecast/chromecast.gni
diff --git a/chromecast/chromecast.gni b/chromecast/chromecast.gni
index 610b179aeb94553483e92a4547f52b135ff87514..3e0d271a825afc5dbf50cc9e7f83cfdf9a189ea1 100644
--- a/chromecast/chromecast.gni
+++ b/chromecast/chromecast.gni
@@ -2,10 +2,34 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+# This args block should contain arguments used within the //chromecast
+# directory. Arguments which are used in other Chrome components should
+# be instead declared in //build/config/chromecast_build.gni.
 declare_args() {
-  # chromecast_branding is used to indicate build version. Set it to
-  # "public" for Chromium build.
+  # chromecast_branding is used to indicate build version. Set it to "public"
+  # for a Chromium build.
   chromecast_branding = "public"

[brettw, 2015/09/17 22:52:14]

Can this be changed in a followup patch to be a boolean? It prevents typos in
the strings from subtly messing everything up. Chrome uses is_chrome_branded for
this, so a is_chromecast_branded would be nicely symmetrics.

[slan, 2015/09/18 02:31:26]

This used to be our convention, but we changed it so that the concept of
"branding" was not constrained to a binary value. We use this variable heavily
in our internal code. I have opened up an internal bug where we can discuss this
further: b/24177554
 

 
+  # True if Chromecast build is targetted for linux desktop.
+  is_chromecast_desktop_build = is_linux && target_cpu != "arm"
+
+  # Use the stub graphics lib in //chromecast/graphics. If this is true, the
+  # value of |libcast_graphics_path| is ignored.
+  use_default_cast_graphics =
+      chromecast_branding == "public" || is_chromecast_desktop_build
+
+  # The path to the cast_graphics shared library. Any target pointed to must
+  # be named "libcast_graphics_1.0".
+  libcast_graphics_path = ""
+
+  # Use the stub media library in //chromecast/media. If this is true, the
+  # value of |libcast_media_path| is ignored.
+  use_default_cast_media =
+      chromecast_branding == "public" || is_chromecast_desktop_build
+
+  # The path to the cast_media shared library. Any target pointed to must be
+  # named "libcast_media_1.0".
+  libcast_media_path = ""
+
   use_playready = false

[brettw, 2015/09/17 22:52:14]

Can you document this while you're changing everything in here?

[slan, 2015/09/18 02:31:26]

Done.

 }