All media router specific code covered with conditional compilation.

This patch adds missed ifdef ENABLE_MEDIA_ROUTER to C++ source files and
corresponding if(enable_media_router) to BUILD.gn files.
Without that, it did not compile if set "enable_media_router = false"
in the features.gni.

[email protected], [email protected], [email protected]
BUG=

Review-Url: https://codereview.chromium.org/2669573002
Cr-Commit-Position: refs/heads/master@{#453585}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index e9dfb5e..0befaac 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -1692,8 +1692,6 @@
       "guest_view/web_view/context_menu_content_type_web_view.h",
       "media/capture_access_handler_base.cc",
       "media/capture_access_handler_base.h",
-      "media/cast_transport_host_filter.cc",
-      "media/cast_transport_host_filter.h",
       "media/extension_media_access_handler.cc",
       "media/extension_media_access_handler.h",
       "media/webrtc/desktop_capture_access_handler.cc",
@@ -1868,6 +1866,12 @@
       "sync_file_system/task_logger.cc",
       "sync_file_system/task_logger.h",
     ]
+    if (enable_media_router) {
+      sources += [
+        "media/cast_transport_host_filter.cc",
+        "media/cast_transport_host_filter.h",
+      ]
+    }
     public_deps += [ "//chrome/browser/extensions" ]
     allow_circular_includes_from += [ "//chrome/browser/extensions" ]
     deps += [