Make sure heap snapshot mocks are evaluated in heap profiler's worker

Some heap profiler test evaluated heap snapshot mocks right in the front-end page. Now that we don't use fake heap snapshot worker in the tests some of the classes are not available in the front-end page and only live inside the worker. This change updates heap profiler tests so that all mocks are evaluated in valid environment.

heapSnapshotLoaderTest moved to heap-snapshot.html next to other tests that use heap snapshot mocks.

BUG=None
R=loislo@chromium.org

Review URL: https://codereview.chromium.org/133273031

git-svn-id: svn://svn.chromium.org/blink/trunk@165384 bbb929c8-8fbe-4397-9dbb-9b2b20218538