Extract ExtensionFunctionRegistry from ExtensionFunctionDispatcher.

Reapply 127159 (http://codereview.chromium.org/9666059) plus important fixes.

Refactor extension_function_dispatcher to extract ExtensionFunctionRegistry.
This allows us to generate an additional code block that takes an ExtensionFunctionRegistry
and asks it to register generated API functions.

Then switch DnsResolve over to get registered this way.

Along the way, notice that DNSResolve is capitalized using an untenable style. Fix that.

Fixes since original 127159:

  - change name of build rule to gen_bundle_api
  - actually add per-file dependencies to .gyp (this was why clean builds
    failed)
  - change 'outputs' to match the emitted filename, fixing a needless
    rebuild problem.
  - split the top-level build action that was a part of
    json_schema_compile.gypi, and include it only in api.gyp, thus fixing
    the problem where json_schema_compiler_tests.gyp was asking it to create
    outputs in the tools/json_schema_compiler_test directory, again causing
    needless work during the build process.

BUG=none (essential plumbing work)
TEST=same as before.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=127555

[asargent_no_longer_on_chrome, 2012-03-16 20:27:50]

lgtm

[bradn, 2012-03-19 19:04:31]

By the way, it looks like the ONLY instance of 'idl' rules that doesn't use msvs
idl has msvs_external_rule turned on, so that strongly suggests it may be broken
without.