base: Change DCHECK_IS_ON to a macro DCHECK_IS_ON() to match Chromium

changes (see http://crrev.com/e649f573) and fix unit test runtime
errors when building with GYP_DEFINES=dcheck_always_on=1.

include/base/internal/cef_thread_checker_impl.h

@@ -37,6 +37,7 @@
 #include "include/base/cef_platform_thread.h"
 
 namespace base {
+namespace cef_internal {
 
 // Real implementation of ThreadChecker, for use in debug mode, or
 // for temporary use in release mode (e.g. to CHECK on a threading issue
@@ -65,6 +66,7 @@ class ThreadCheckerImpl {
   mutable PlatformThreadRef valid_thread_id_;
 };
 
+}  // namespace cef_internal
 }  // namespace base
 
 #endif  // CEF_INCLUDE_BASE_INTERNAL_THREAD_CHECKER_IMPL_H_