Pass 'name' to value getters in InspectorBackendDispatcher as const char*

This avoids generating code for the literal -> WTF::String implicit
conversions in all callsites.

Review URL: https://codereview.chromium.org/247193004

git-svn-id: svn://svn.chromium.org/blink/trunk@172143 bbb929c8-8fbe-4397-9dbb-9b2b20218538