Loads CastEglPlatform implementation from shared library.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index b0dbfb8ac9fe134b1df5cba55e5a703e85eb3feb..a6dcd64f470b916e218237f9897e2f5ddfa7dd5a 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -1516,6 +1516,7 @@
 
     # Ozone platforms to include in the build.
     'ozone_platform_caca%': 0,
+    'ozone_platform_cast%': 0,
     'ozone_platform_dri%': 0,
     'ozone_platform_drm%': 0,
     'ozone_platform_egltest%': 0,
@@ -1850,6 +1851,9 @@
           }],
         ],
       }],
+      ['chromecast==1 and OS!="android"', {
+        'ozone_platform_cast%': 1
+      }],
       ['OS=="linux" and target_arch!="mipsel"', {
         'clang%': 1,
       }],  # OS=="mac"