Fix extensions.gyp.

This adds a missing change from
https://crrev.com/680be408457f4272b468e72468eb22e1c0f0b67a

NOTRY=true
NOTREECHECKS=true

Review URL: https://codereview.chromium.org/673773003

Cr-Commit-Position: refs/heads/master@{#301031}

extensions/extensions.gyp

@@ -252,8 +252,8 @@
         'common/view_type.h',
         '<(SHARED_INTERMEDIATE_DIR)/extensions/common/mojo/keep_alive.mojom.cc',
         '<(SHARED_INTERMEDIATE_DIR)/extensions/common/mojo/keep_alive.mojom.h',
-        '<(SHARED_INTERMEDIATE_DIR)/extensions/common/stash.mojom.cc',
-        '<(SHARED_INTERMEDIATE_DIR)/extensions/common/stash.mojom.h',
+        '<(SHARED_INTERMEDIATE_DIR)/extensions/common/mojo/stash.mojom.cc',
+        '<(SHARED_INTERMEDIATE_DIR)/extensions/common/mojo/stash.mojom.h',
       ],
       # Disable c4267 warnings until we fix size_t to int truncations.
       'msvs_disabled_warnings': [ 4267, ],