[sheriff] Fix DEPS for subresource_filter.

There was a flaky failure in compiling
components/subresource_filter/content/browser/subresource_filter_client.h

See:
https://ci.chromium.org/p/chromium/builders/ci/win32-rel/12234

Error message was that it couldn't find:
components/subresource_filter/core/mojom/subresource_filter.mojom.h

Speculatively fixing this issue by adding the mojom file to DEPS.

TBR=sky@chromium.org

Change-Id: I72668d5e8d12af8d6cb32fae4b8258c4b1b62bd2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1502332Reviewed-by: Darren Shen <shend@chromium.org>
Commit-Queue: Darren Shen <shend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637594}

components/subresource_filter/content/browser/BUILD.gn

@@ -47,6 +47,7 @@ static_library("browser") {
     "//components/subresource_filter/content/mojom",
     "//components/subresource_filter/core/browser",
     "//components/subresource_filter/core/common",
+    "//components/subresource_filter/core/mojom",
     "//components/ukm:ukm",
     "//content/public/browser",
     "//content/public/common",