Add a cc_library libwvpl_cas_proxy target.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=227702338

media_cas_proxy_sdk/external/common/wvpl/BUILD

@@ -26,6 +26,16 @@ cc_binary(
     ],
 )
 
+cc_library(
+    name = "libwvpl_cas_proxy",
+    srcs = [":libwvpl_cas_proxy.so"],
+    hdrs = glob(["*.h"]),
+    deps = [
+        "//base",
+        "//sdk/external/common/wvpl:sdk",
+    ],
+)
+
 cc_library(
     name = "wvpl_cas_proxy_session",
     srcs = [