Make layout test harness extensible with custom layout tests directory

third_party/WebKit/Source/devtools/layout_tests/SlowTests

Index: third_party/WebKit/Source/devtools/layout_tests/SlowTests
diff --git a/third_party/WebKit/Source/devtools/layout_tests/SlowTests b/third_party/WebKit/Source/devtools/layout_tests/SlowTests
new file mode 100644
index 0000000000000000000000000000000000000000..afb807e200ebf4db8eec1eae86b33965952564c3
--- /dev/null
+++ b/third_party/WebKit/Source/devtools/layout_tests/SlowTests
@@ -0,0 +1,43 @@
+crbug.com/451577 [ Mac ] inspector/extensions/extensions-reload.html [ Slow ]
+crbug.com/451577 [ Mac ] inspector/extensions/extensions-resources.html [ Slow ]
+crbug.com/451577 [ Win10 ] inspector/extensions/extensions-sidebar.html [ Slow ]
+crbug.com/451577 [ Mac ] inspector/layers/layer-canvas-log.html [ Slow ]
+crbug.com/451577 [ Mac ] inspector/network/network-domain-filter.html [ Slow ]
+# Most inspector tests are slow in Debug.
+webkit.org/b/90488 [ Debug ] inspector/ [ Slow ]
+webkit.org/b/90488 [ Debug ] http/tests/inspector/ [ Slow ]
+webkit.org/b/90488 [ Debug ] http/tests/inspector-enabled/ [ Slow ]
+crbug.com/451577 inspector/console [ Slow ]
+crbug.com/451577 [ Win ] http/tests/inspector/network/network-datareceived.html [ Slow ]
+crbug.com/450493 inspector/sources/ [ Slow ]
+crbug.com/450493 inspector-enabled/sources/ [ Slow ]
+crbug.com/450493 http/tests/inspector/sources/ [ Slow ]
+crbug.com/450493 http/tests/inspector/stacktraces/ [ Slow ]
+crbug.com/450493 inspector/profiler/ [ Slow ]
+crbug.com/420008 inspector/tracing/ [ Slow ]
+crbug.com/420008 virtual/threaded/inspector/tracing/ [ Slow ]
+crbug.com/246190 [ Release ] http/tests/inspector/indexeddb/ [ Slow ]
+crbug.com/451577 [ Mac ] inspector/extensions/extensions-sidebar.html [ Slow ]
+crbug.com/451577 [ Mac ] inspector/extensions/extensions-events.html [ Slow ]
+webkit.org/b/90488 [ Release ] http/tests/inspector/compiler-source-mapping-debug.html [ Slow ]
+crbug.com/243492 http/tests/inspector-enabled/injected-script-discard.html [ Slow ]
+crbug.com/327078 http/tests/inspector/network/long-script-content.html [ Slow ]
+crbug.com/420008 [ Release ] inspector/editor/text-editor-word-jumps.html [ Slow ]
+crbug.com/420008 [ Release ] http/tests/inspector/console-xhr-logging.html [ Slow ]
+crbug.com/596486 [ Linux ] inspector/elements/insert-node.html [ Slow ]
+webkit.org/b/84735 [ Win ] http/tests/inspector/change-iframe-src.html [ Slow ]
+crbug.com/504565 [ Mac ] http/tests/inspector/search/sources-search-scope.html [ Slow ]
+crbug.com/451577 http/tests/inspector/resource-tree/resource-tree-crafted-frame-add.html [ Slow ]
+crbug.com/451577 http/tests/inspector/resource-tree/resource-tree-frame-in-crafted-frame.html [ Slow ]
+crbug.com/510337 inspector/elements/styles-1/edit-value-url-with-color.html [ Slow ]
+crbug.com/246749 inspector/extensions/extensions-panel.html [ Slow ]
+crbug.com/336481 inspector/jump-to-previous-editing-location.html [ Slow ]
+crbug.com/510337 inspector/console/console-format.html [ Slow ]
+crbug.com/504706 [ Linux ] inspector/profiler/heap-snapshot-containment-expansion-preserved-when-sorting.html [ Slow ]
+crbug.com/504706 [ Linux ] inspector/profiler/heap-snapshot-containment-sorting.html [ Slow ]
+crbug.com/480769 http/tests/inspector/service-workers/service-workers-redundant.html [ Slow ]
+crbug.com/480769 http/tests/inspector/service-workers/service-worker-agents.html [ Slow ]
+crbug.com/535478 [ Win ] virtual/threaded/inspector/tracing/decode-resize.html [ Slow ]
+crbug.com/548765 http/tests/inspector/console-fetch-logging.html [ Slow ]
+crbug.com/528419 [ Linux ] inspector/elements/shadow/shadow-host-display-modes.html [ Slow ]
+crbug.com/528419 inspector/elements/styles-2/pseudo-elements.html [ Slow ]