[blink/script] Add trace events for PendingScripts

This CL adds the following trace events in the blink category:
- PendingScript::ExecuteScriptBlock
- ScriptRunner::ExecuteInOrderTask
- ScriptRunner::ExecuteAsyncTask
- ClassicPendingScript::GetSource

Bug: 865098
Change-Id: I4b8af61283bd97b0ab1d9e0b74fc0f08ce7a2293
Reviewed-on: https://chromium-review.googlesource.com/c/1356545
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Hiroshige Hayashizaki <hiroshige@chromium.org>
Cr-Commit-Position: refs/heads/master@{#613047}
3 files changed