[DevTools] Added more null check into DispatcherBase template

R=dgozman@chromium.org

Review-Url: https://codereview.chromium.org/2327273002
Cr-Original-Commit-Position: refs/heads/master@{#417848}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 9ff4610e4b671ac11b79e3d0ad9e4ef934da5a71
1 file changed