Use 10Mb chunks when writing heap snapshot to temp file
Use 10Mb chunks when writing heap snapshot to temp file

This speeds up writing to the temp file about 15x

BUG=324769
R=loislo@chromium.org

Review URL: https://codereview.chromium.org/107593004

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@164319 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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