Use PAGE_MAX_SIZE. PAGE_SIZE is now a variable size.

This fixes exception_handler.cc:77:8: error: fields must have a constant size:
'variable length array in structure' extension will never be supported
  char protected_buffer[PAGE_SIZE] __attribute__((aligned(PAGE_SIZE)));

BUG=None
TEST=breakpad builds on ios8
R=mark@chromium.org

Review URL: https://breakpad.appspot.com/9654002

Patch from Justin Cohen <justincohen@chromium.org>.

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1338 4c0a9323-5329-0410-9bdc-e9ce6186880e