[mojo] include mojo header in /chrome/browser/extensions

This is preparation CL to use forward declaration only header in mojo's
generated code.
If we include forward declaration only header in mojo's generated code, we need
to include mojo header files in some places where definition is necessary.

master CL is in
https://chromium-review.googlesource.com/c/chromium/src/+/1438975

CC=rockot@google.com

This CL was uploaded by git cl split.

R=lazyboy@chromium.org

Bug: 922875
Change-Id: I7458979e42596e5b0451d95263af37c82921e156
Reviewed-on: https://chromium-review.googlesource.com/c/1447136
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Istiaque Ahmed <lazyboy@chromium.org>
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#627685}

chrome/browser/extensions/test_blacklist_state_fetcher.cc

@@ -8,6 +8,7 @@
 #include "base/threading/thread_task_runner_handle.h"
 #include "components/safe_browsing/db/v4_test_util.h"
 #include "services/network/public/cpp/shared_url_loader_factory.h"
+#include "services/network/public/mojom/url_loader.mojom.h"
 
 namespace extensions {
 namespace {