Enable external V8 snapshot on Android through GN.

content/test/BUILD.gn

Index: content/test/BUILD.gn
diff --git a/content/test/BUILD.gn b/content/test/BUILD.gn
index 80e75581140ca27161aef07b8874fb96163b8e4f..b3a4065e6c19dca5623b3c1f7fda047a5edc6cc6 100644
--- a/content/test/BUILD.gn
+++ b/content/test/BUILD.gn
@@ -4,6 +4,7 @@
 
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
+import("//build/module_args/v8.gni")
 
 content_tests_gypi_values = exec_script(
     "//build/gypi_to_gn.py",
@@ -146,6 +147,9 @@ static_library("test_support") {
       "test/test_content_client.cc",
     ]
   }
+  if (v8_use_external_startup_data) {
+    deps += [ "//gin:gin" ]
+  }
 }
 
 if (!is_ios) {