DevTools: eliminate 1k lines of generated code in InspectorBackendDispatcher.cpp

and reduce binary footprint by 5% ~25kb of 587k (clang x64 release)

BUG=382569
R=yurys@chromium.org

Review URL: https://codereview.chromium.org/325833002

git-svn-id: svn://svn.chromium.org/blink/trunk@175877 bbb929c8-8fbe-4397-9dbb-9b2b20218538