Move enable extensions define to a build flag.

Removes the global define and convert to a more scaleable build flag system.

The json_schema_compiler tests were moved from the unit tests target to one on their directory with an extensions-only dependency on the new test target.

Review-Url: https://codereview.chromium.org/2479593006
Cr-Commit-Position: refs/heads/master@{#431741}
diff --git a/chrome/browser/net/chrome_network_delegate.cc b/chrome/browser/net/chrome_network_delegate.cc
index 340d903f..3543941d 100644
--- a/chrome/browser/net/chrome_network_delegate.cc
+++ b/chrome/browser/net/chrome_network_delegate.cc
@@ -48,6 +48,7 @@
 #include "content/public/browser/resource_request_info.h"
 #include "content/public/common/content_switches.h"
 #include "content/public/common/process_type.h"
+#include "extensions/features/features.h"
 #include "net/base/host_port_pair.h"
 #include "net/base/load_flags.h"
 #include "net/base/net_errors.h"
@@ -71,7 +72,7 @@
 #include "chrome/common/chrome_switches.h"
 #endif
 
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
 #include "extensions/common/constants.h"
 #endif