Support full range of PreflightPolicy over WebURLLoaderOptions

Allow users of WebURLLoader to state the preflight behavior to follow
for the request. This is done so that the user/caller can explicitly
control when its author header set
(http://www.w3.org/TR/cors/#author-request-headers) is empty, then no
preflight must be performed.

This puts the responsibility on the caller to adhere to CORS and not
disable preflighting when the author set is non-empty or the request
is over non-simple methods (http://www.w3.org/TR/cors/#simple-method )

The WebURLLoaderOptions default is ConsiderPreflight.

R=jochen
BUG=173727

Review URL: https://codereview.chromium.org/68173029

git-svn-id: svn://svn.chromium.org/blink/trunk@162225 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Replace deprecated call to V8 SetDefaultResourceConstraintsForCurrentPlatform with ResourceConstraints::ConfigureDefaults.

Also replace call to 1 argument SetResourceConstraints function with 2 argument
function.

BUG=312241

Review URL: https://codereview.chromium.org/75163004

git-svn-id: svn://svn.chromium.org/blink/trunk@162226 bbb929c8-8fbe-4397-9dbb-9b2b20218538