Fix up dependencies for FetchAPIRequestBody typemap

This patch adds the right dependency to fix the build error described
by the below bug.

Bug: 1122770
Change-Id: I943e10ef4b10750d01bd4c1ce47bc9f4f0e0816c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2368455Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Nicolas Arciniega <niarci@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#803177}

third_party/blink/public/mojom/BUILD.gn

@@ -555,6 +555,8 @@ mojom("mojom_platform") {
         "//third_party/blink/renderer/platform/loader/fetch/resource_request.h",
       ]
       traits_private_headers = [ "//third_party/blink/renderer/platform/loader/fetch/fetch_api_request_body_mojom_traits.h" ]
+      traits_deps =
+          [ "//third_party/blink/renderer/platform/network:make_generated" ]
     },
     {
       types = [

third_party/blink/renderer/platform/network/BUILD.gn

@@ -14,6 +14,7 @@ make_names("http_names") {
 group("make_generated") {
   visibility = [
     ":*",
+    "//third_party/blink/public/mojom:mojom_platform_blink",
     "//third_party/blink/renderer/platform:*",
   ]