Make the snapshot a public dependency of v8.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 5a743606293a1edfc546cf532be2bcc1fb19634a..b045d09ffcf51352f2ff4b2f9c36a7f385598634 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -474,9 +474,13 @@ source_set("v8_snapshot") {
     ":js2c",
     ":js2c_experimental",
     ":js2c_extras",
-    ":run_mksnapshot",
     ":v8_base",
   ]
+  public_deps = [
+    # This should be public so downstream targets can declare the snapshot
+    # output file as their inputs.
+    ":run_mksnapshot",
+  ]
 
   sources = [
     "$target_gen_dir/libraries.cc",
@@ -502,9 +506,11 @@ if (v8_use_external_startup_data) {
       ":js2c",
       ":js2c_experimental",
       ":js2c_extras",
-      ":run_mksnapshot",
       ":v8_base",
+    ]
+    public_deps = [
       ":natives_blob",
+      ":run_mksnapshot",
     ]
 
     sources = [
@@ -1574,6 +1580,10 @@ if (component_mode == "shared_library") {
     } else if (v8_use_snapshot) {
       deps = [
         ":v8_base",
+      ]
+      # v8_snapshot should be public so downstream targets can declare the
+      # snapshot file as their input.
+      public_deps = [
         ":v8_snapshot",
       ]
     } else {
@@ -1609,6 +1619,8 @@ if (component_mode == "shared_library") {
     } else if (v8_use_snapshot) {
       deps = [
         ":v8_base",
+      ]
+      public_deps = [
         ":v8_snapshot",
       ]
     } else {