Move js perf tests to a common root on the perf dashboard.

BUG=
R=dslomov@chromium.org

Review URL: https://codereview.chromium.org/667373004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24806 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

test/js-perf-test/Classes/Classes.json

 {
+  "name": "JSTests/Classes",
   "path": ["."],
   "main": "run.js",
   "flags": ["--harmony-classes"],

test/js-perf-test/Collections/Collections.json

 {
+  "name": "JSTests/Collections",
   "path": ["."],
   "main": "run.js",
   "flags": ["--harmony-collections"],

test/js-perf-test/Iterators/Iterators.json

 {
+  "name": "JSTests/Iterators",
   "path": ["."],
   "main": "run.js",
   "run_count": 5,

test/js-perf-test/Strings/Strings.json

 {
+  "name": "JSTests/Strings",
   "path": ["."],
   "main": "run.js",
   "flags": ["--harmony-strings"],