Add toolset support to dump_dependency_json.
Add toolset support to dump_dependency_json.

dump_dependency_json was only outputting #target targets, not #host. Add
generator_supports_multiple_toolsets to get it to do the right thing.
The resulting dependency info appears to be correct without any code
changes.

Review URL: http://codereview.chromium.org/10182004/
Patch from Richard Coles <torne@chromium.org>!
witwall/gyp,witwall/gyp,witwall/gyp,witwall/gyp,witwall/gyp