Certificate Transparency: Add STH Fetching capability.

components/certificate_transparency/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-source_set("logging") {
+source_set("certificate_transparency") {
   sources = [
-    "log_buffer.cc",
-    "log_buffer.h",
-    "logging.cc",
-    "logging.h",
+    "log_proof_fetcher.cc",
+    "log_proof_fetcher.h",
   ]
 
   deps = [
     "//base",
+    "//components/safe_json",
+    "//net",
+    "//url",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
-    "logging_unittest.cc",
+    "log_proof_fetcher_unittest.cc",
   ]
 
   deps = [
+    ":certificate_transparency",
     "//base/test:test_support",
     "//testing/gtest",
   ]
 }