Store heap snapshot in a temp file

Protocol data of heap snapshot is saved in a temp file so that it can be later saved in a user specified file. This resembles similar behaviour of CPU profiler and required for not storing heap snapshots on the backend.

BUG=324769
R=loislo@chromium.org

Review URL: https://codereview.chromium.org/120913002

git-svn-id: svn://svn.chromium.org/blink/trunk@164316 bbb929c8-8fbe-4397-9dbb-9b2b20218538