NTP: Extract JSON requests from Fetcher.

components/ntp_snippets/BUILD.gn

Index: components/ntp_snippets/BUILD.gn
diff --git a/components/ntp_snippets/BUILD.gn b/components/ntp_snippets/BUILD.gn
index b37377db155cefdfc0da47d1def5ab280734652d..b8b320a63302d269520c8a39b5b63c043771c029 100644
--- a/components/ntp_snippets/BUILD.gn
+++ b/components/ntp_snippets/BUILD.gn
@@ -49,6 +49,10 @@ static_library("ntp_snippets") {
     "remote/ntp_snippet.h",
     "remote/ntp_snippets_fetcher.cc",
     "remote/ntp_snippets_fetcher.h",
+    "remote/ntp_snippets_json_request.cc",
+    "remote/ntp_snippets_json_request.h",
+    "remote/ntp_snippets_request_params.cc",
+    "remote/ntp_snippets_request_params.h",
     "remote/ntp_snippets_scheduler.h",
     "remote/remote_suggestions_database.cc",
     "remote/remote_suggestions_database.h",
@@ -124,6 +128,7 @@ source_set("unit_tests") {
     "physical_web_pages/physical_web_page_suggestions_provider_unittest.cc",
     "remote/ntp_snippet_unittest.cc",
     "remote/ntp_snippets_fetcher_unittest.cc",
+    "remote/ntp_snippets_json_request_unittest.cc",
     "remote/remote_suggestions_database_unittest.cc",
     "remote/remote_suggestions_provider_unittest.cc",
     "remote/remote_suggestions_status_service_unittest.cc",