Revert of [gin] Unify snapshot loading on Windows and other platforms.

gin/BUILD.gn

Index: gin/BUILD.gn
diff --git a/gin/BUILD.gn b/gin/BUILD.gn
index 88fa40a8b3b6d0298e0ba97356aeb030ce3243a6..4da04284e3f69845f17428ae65d45b656bab758f 100644
--- a/gin/BUILD.gn
+++ b/gin/BUILD.gn
@@ -86,12 +86,47 @@
     "//base/third_party/dynamic_annotations",
     "//crypto",
   ]
+  if (v8_use_external_startup_data && is_win) {
+    public_deps += [ ":gin_v8_snapshot_fingerprint" ]
+    sources += [ "$target_gen_dir/v8_snapshot_fingerprint.cc" ]
+    defines += [ "V8_VERIFY_EXTERNAL_STARTUP_DATA" ]
+  }
 
   if (is_mac) {
     libs = [ "CoreFoundation.framework" ]
   }
 
   configs += [ "//v8:external_startup_data" ]
+}
+
+if (v8_use_external_startup_data) {
+  action("gin_v8_snapshot_fingerprint") {
+    script = "//gin/fingerprint/fingerprint_v8_snapshot.py"
+
+    snapshot_file = "$root_out_dir/snapshot_blob.bin"
+    natives_file = "$root_out_dir/natives_blob.bin"
+    output_file = "$target_gen_dir/v8_snapshot_fingerprint.cc"
+
+    args = [
+      "--snapshot_file",
+      rebase_path(snapshot_file, root_build_dir),
+      "--natives_file",
+      rebase_path(natives_file, root_build_dir),
+      "--output_file",
+      rebase_path(output_file, root_build_dir),
+    ]
+    inputs = [
+      snapshot_file,
+      natives_file,
+    ]
+    outputs = [
+      output_file,
+    ]
+
+    deps = [
+      "//v8",
+    ]
+  }
 }
 
 executable("gin_shell") {