Enable rwt log for blink_web_tests

So that we can get data for phantom overhead. We can also
find potential area for performance improvement.

Bug: 982208
Change-Id: I72a856701d4a8bb7e1b1982fc176e20c2706c2cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2976545
Reviewed-by: Dirk Pranke <[email protected]>
Commit-Queue: Weizhong Xia <[email protected]>
Cr-Commit-Position: refs/heads/master@{#894435}
diff --git a/BUILD.gn b/BUILD.gn
index e59f34c0..a12740b 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1211,6 +1211,7 @@
   _common_web_test_args += [
     "--seed",
     "4",
+    "--debug-rwt-logging",
     "--no-show-results",
     "--zero-tests-executed-ok",
     "--clobber-old-results",