This CL removes a number of tests that we don't plan to port to Dart:
1) custom-elements. We're going to use a different mechanism for custom
elements. We'll need to write a new set of tests as we implement it.
2) inspector. These are tests of the JS inspector backend, which we don't
plan to use.
3) js. This is a test of a JavaScript feature.
4) mocha. These are tests of the JavaScript testing framework we were using.
5) mutation-observer. We're keeping the C++ code for mutation observers, but
it's unclear how we want to expose this in the platform.
6) resources. These are JavaScript-based testing frameworks.
R=eseidel@chromium.org, ojan@chromium.org
Review URL: https://codereview.chromium.org/920343002
d7ee97cc3d