Add check_targets list to .gn.

Start trying to pass "gn check".

Change-Id: Iec694d8abf558f3e1ca477dd3934020088e43cb5
Reviewed-on: https://pdfium-review.googlesource.com/c/43895
Reviewed-by: Henrique Nakashima <hnakashima@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/samples/BUILD.gn b/samples/BUILD.gn
index 30cc8ef..909de2e 100644
--- a/samples/BUILD.gn
+++ b/samples/BUILD.gn
@@ -58,10 +58,12 @@
   configs += [ ":pdfium_samples_config" ]
 
   if (pdf_enable_v8) {
-    deps += [ "//v8:v8_libplatform" ]
+    deps += [
+      "//v8:v8_headers",
+      "//v8:v8_libplatform",
+    ]
     include_dirs = [
       "//v8",
-      "//v8/include",
     ]
     configs += [ "//v8:external_startup_data" ]
   }