Pepper: Don't check quota for origins with unlimited storage.

PepperFileSystemBrowserHost now checks for origins with
unlimited storage before consructing the quota reservation
system.

PepperFileIOHost now uses the file system ChecksQuota to
determine if file descriptors with write access can safely be
passed to the plugin.

BUG=327590

Review URL: https://codereview.chromium.org/99103010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240177 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240177