Duplicating load_library_perf_tests isolate

For the new perf recipe we are going to need to create duplicate isolates
for each test suite that we run until migration is complete.  This is becuase
the script target is different in the new perf recipe.

Turns out that in gn_isolate_map.pyl the entry has to be the same name as the
label or the test won't run.  See failing build: https://uberchromegw.corp.google.com/i/chromium.perf.fyi/builders/Mac%20Builder%20FYI/builds/608

 Please advise if there is another way to reuse the isolate without duplicating the entries.

Change-Id: Id7adddc9621bc5749a2d7377766d1d78669d238c
Reviewed-on: https://chromium-review.googlesource.com/989844Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Emily Hanley <eyaich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547719}

chrome/test/BUILD.gn

@@ -5450,6 +5450,47 @@ if (!is_android && !is_fuchsia) {
     assert_no_deps = [ "//chrome" ]
   }
 
+  # Executable to measure time to load libraries.
+  test("load_library_perf_tests_v2") {
+    sources = [
+      "../browser/load_library_perf_test.cc",
+    ]
+
+    # This test deliberately does not depend in chrome's test support targets.
+    # This is a small test and Chrome's test support targets bring in the
+    # world, causing link time to explode. Please don't add more dependencies
+    # here without understanding how it affects link time (and factor them
+    # differently if possible).
+    deps = [
+      "//base/test:test_support_perf",
+      "//media:media_buildflags",
+      "//testing/gtest",
+      "//testing/perf",
+      "//third_party/widevine/cdm:headers",
+    ]
+
+    if (enable_library_cdms) {
+      deps += [ "//media/cdm:cdm_paths" ]
+      data_deps = [
+        "//media/cdm/library_cdm/clear_key_cdm",
+        "//third_party/widevine/cdm",
+      ]
+    }
+
+    data = [
+      # Needed for isolate script to execute.
+      "//testing/scripts/common.py",
+      "//testing/xvfb.py",
+      "//testing/scripts/run_gtest_perf_test.py",
+      "//testing/scripts/run_performance_tests.py",
+      "//testing/scripts/run_telemetry_benchmark_as_googletest.py",
+      "//tools/perf/generate_legacy_perf_dashboard_json.py",
+    ]
+
+    # This target should not require the Chrome executable to run.
+    assert_no_deps = [ "//chrome" ]
+  }
+
   # Executable to measure time to load libraries.
   test("load_library_perf_tests") {
     sources = [

testing/buildbot/gn_isolate_map.pyl

@@ -1153,7 +1153,7 @@
     ],
   },
   "load_library_perf_tests_v2": {
-    "label": "//chrome/test:load_library_perf_tests",
+    "label": "//chrome/test:load_library_perf_tests_v2",
     "type": "script",
     "script": "//testing/scripts/run_performance_tests.py",
     "args": [