Add external/wpt/common/ to blink_web_tests_support_data

Needed for reftests in webgpu_blink_web_tests (in an upcoming CL).

Bug: 1061273
Change-Id: I23af7b08506f173388c39ae9972b69836a419853
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2209386
Auto-Submit: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#770581}

BUILD.gn

@@ -1098,6 +1098,7 @@ if (!is_ios) {
       "//third_party/blink/tools/",
       "//third_party/blink/web_tests/VirtualTestSuites",
       "//third_party/blink/web_tests/external/WPT_BASE_MANIFEST_8.json",
+      "//third_party/blink/web_tests/external/wpt/common/",
       "//third_party/blink/web_tests/external/wpt/resources/",
       "//third_party/blink/web_tests/resources/",
       "//third_party/blink/web_tests/wpt_internal/",