DevTools: Fix the way extremely long script content is loaded on page reload.

BUG=255592

Review URL: https://chromiumcodereview.appspot.com/18316005

git-svn-id: svn://svn.chromium.org/blink/trunk@153625 bbb929c8-8fbe-4397-9dbb-9b2b20218538
virtual/gpu/fast/canvas/canvas-blend-{solid,image}.html flaky failure on mac

TBR=cabanier@adobe.com
NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/18459007

git-svn-id: svn://svn.chromium.org/blink/trunk@153626 bbb929c8-8fbe-4397-9dbb-9b2b20218538