Move webkitpy/w3c to blinkpy/w3c.

* Add webkitpy/common/add_blinkpy.py to help blinkpy.w3c dependency from
  webkitpy.

* This CL doesn't sort import directives intentionally because we'll
  change other webkitpy" to "blinkpy" soon.

Change-Id: Ieb2d8617e10b4d8a10136bd7924022a51ee37571
Reviewed-on: https://chromium-review.googlesource.com/1014921
Reviewed-by: Nico Weber <[email protected]>
Reviewed-by: Quinten Yearsley <[email protected]>
Commit-Queue: Kent Tamura <[email protected]>
Cr-Commit-Position: refs/heads/master@{#551919}
diff --git a/BUILD.gn b/BUILD.gn
index a9199a1b..06c117e 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -960,6 +960,7 @@
       "//third_party/WebKit/LayoutTests/",
       "//third_party/WebKit/Tools/Scripts/",
       "//third_party/blink/perf_tests/",
+      "//third_party/blink/tools/",
       "//third_party/pywebsocket/",
     ]