build: Add VAAPI decode binary.

BUG=chromium:1062407,b:175909299

Change-Id: I6cb71aa9f13f252bde352a4b558acef1eb354a12
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2601546Reviewed-by: Miguel Casas <mcasas@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Jao-ke Chin-Lee <jchinlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#839468}

BUILD.gn

@@ -951,7 +951,10 @@ if (is_chromeos_ash) {
         "//media/gpu:video_encode_accelerator_unittest",
       ]
       if (use_vaapi) {
-        data_deps += [ "//media/gpu/vaapi:vaapi_unittest" ]
+        data_deps += [
+          "//media/gpu/vaapi:decode_test",
+          "//media/gpu/vaapi:vaapi_unittest",
+        ]
       }
     }
   }