Add partial pre-read functionality to browser startup (Windows).

PartialPreReadImage has much the smae interface as PreReadImage except the bytes to read becomes a percentage to read and it reads a certain percentage of each section in the binary.

Also adds some unittest coverage.

BUG=chromium:98508
TEST=

Review URL: http://codereview.chromium.org/9235053

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@120371 0039d316-1c4b-4281-b951-d872f2087c98
6 files changed