We need script source for:
- calculating hash to report as part of scriptParsed event,
- reporting it as response on getScriptSource request,
- searching inside as response on searchInContent request,
- breakpoints hints.

In all cases there is no need to store source on inspector side.

R=alph@chromium.org

Bug: chromium:873865,v8:7731
Cq-Include-Trybots: luci.chromium.try:linux_chromium_headless_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ice24ddc72cfff36fb9a2dff2d7c4543defe3f668
Reviewed-on: https://chromium-review.googlesource.com/1182603
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55286}