Build public cast_shell on x86 with GN.

chromecast/build/args.gn

Index: chromecast/build/args.gn
diff --git a/chromecast/build/args.gn b/chromecast/build/args.gn
index 1624b0a9a6b0eb17df4de7d886312dfea369939b..b8a668042e4bbfaf47909aab6f50bf10f8c82004 100644
--- a/chromecast/build/args.gn
+++ b/chromecast/build/args.gn
@@ -3,11 +3,41 @@
 
 root_extra_deps = [ "//chromecast" ]
 
-# Flags set from build/common.gypi
+# See //build/config/features.gni for information on this variable.
+# When this is enabled, the ENABLE_BROWSER_CDMS macro gets defined, which
+# in turn builds //content/browser/render_host/render_process_host_impl.h's

[gunsch, 2015/08/04 00:43:10]

why is this detail here? This flag isn't an arbitrary setting to allow building.
We quite rely on browser-based CDMs.

[slan, 2015/08/04 21:22:04]

Simplified.

+# GetBrowserCdm().
+enable_browser_cdms = true
+
+# TODO(slan): Add note about this variable.
 enable_mpeg2ts_stream_parser = true
+
+# See //build/common.gypi and note that this gets set to "ChromeOS" when
+# chromecast==1. If you omit this, ffmpeg_branding defaults to "Chromium", only
+# registering a subset of required codecs in
+# //src/third_party/ffmpeg/libavcodec/allcodecs.c.
+# Instead of maintaining a separate "Chromecast" ffmpeg branding, "ChromeOS" is
+# used, as it sufficiently covers all the required codecs.
 ffmpeg_branding = "ChromeOS"
+
+# Setting this to true generates libeglplatform_shim.so.1 from
+# //ui/ozone/platform/egltest:egl_platform_x11, which is loaded in
+# OzonePlatformEgltest::LoadShim().
+ozone_platform_ozonex = true
+
+# See the corresponding TODO(gyp) comment in //build/config/features.gni.

[gunsch, 2015/08/04 00:43:10]

Unclear to me if this TODO will remain, since Brett has expressed not wanting us
to introduce a global "is_chromecast".

[slan, 2015/08/04 21:22:04]

This comment is confusing anyway. We can move forward without |is_chromecast|

+# Setting this to true defines the USE_PROPRIETARY_CODECS macro and the proper
+# EME_CODEC macros in //media/base/eme_constants.h.
 proprietary_codecs = true
-enable_browser_cdms = true
+
+# See //build/config/ui.gni. Notice that use_x11 = is_linux && !use_ozone.
+# Without setting use_ozone to true, this make use_x11 = true and the
+# USE_X11 macro to be defined. This in turn causes us to go down the wrong
+# code path in //ui/base/ime/input_method_factory.cc:CreateInputMethod().
+# "return make_scoped_ptr(new InputMethodAuraLinux(delegate));"
+# instead of
+# "return make_scoped_ptr(new InputMethodMinimal(delegate));"
+use_ozone = true
 # TODO(halliwell): look into supporting Cast Ozone with GN.
 # ozone_platform_cast = 1
 # TODO(gyp): Add support for blink_logging_always_on and enable it.