DevTools: _base64ToSize doesn't check content param for null.
DevTools: _base64ToSize doesn't check content param for null.

BUG=425514

Review URL: https://codereview.chromium.org/672573002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@184170 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs