[sdk] Properly add target-specific files to gen_snapshot atom.

Bug: DX-1257 #done
Change-Id: I3d78763549e294cdcdd068efcbc873433e4342c4
diff --git a/public/sdk/fuchsia_dart.api b/public/sdk/fuchsia_dart.api
index 1167130..408e6d1 100644
--- a/public/sdk/fuchsia_dart.api
+++ b/public/sdk/fuchsia_dart.api
@@ -32,4 +32,4 @@
 sdk://fidl/fuchsia.ui.viewsv1token
 sdk://tools/dart_kernel_compiler
 sdk://tools/fidlgen_dart
-sdk://tools/gen_snapshot_x64
\ No newline at end of file
+sdk://tools/gen_snapshot
\ No newline at end of file
diff --git a/runtime/dart/BUILD.gn b/runtime/dart/BUILD.gn
index 4c2738a..db13c06 100644
--- a/runtime/dart/BUILD.gn
+++ b/runtime/dart/BUILD.gn
@@ -98,20 +98,29 @@
 }
 
 sdk_atom("gen_snapshot_sdk") {
-  id = "sdk://tools/gen_snapshot_${current_cpu}"
+  id = "sdk://tools/gen_snapshot"
   category = "partner"
 
+  files_content = [
+    "tools/gen_snapshot.${current_cpu}",
+    "tools/gen_snapshot_product.${current_cpu}",
+  ]
+
   meta = {
     schema = "host_tool"
-    dest = "tools/gen_snapshot_${current_cpu}-meta.json"
+    dest = "tools/gen_snapshot-meta.json"
     value = {
       type = "host_tool"
-      name = "gen_snapshot_${current_cpu}"
+      name = "gen_snapshot"
       root = "tools"
-      files = [
-        "tools/gen_snapshot.${current_cpu}",
-        "tools/gen_snapshot_product.${current_cpu}",
-      ]
+      target_files = {}
+      if (target_cpu == "arm64") {
+        target_files.arm64 = files_content
+      } else if (target_cpu == "x64") {
+        target_files.x64 = files_content
+      } else {
+        assert(false, "Unknown CPU type: $target_cpu")
+      }
     }
   }