This patch implements a mechanism for more granular link URL permissions (filtering on scheme/host). This fixes the bug that allowed PDFs to have working links to any "chrome://" URLs.

BUG=528505,226927

Review URL: https://codereview.chromium.org/1362433002

Cr-Commit-Position: refs/heads/master@{#351705}
  void RevokeAllPermissionsForFile(const base::FilePath& file) {
    base::FilePath stripped = file.StripTrailingSeparators();
    file_permissions_.erase(stripped);
    request_file_set_.erase(stripped);
  }

  void RevokeAllPermissionsForFile(const base::FilePath& file) {
    base::FilePath stripped = file.StripTrailingSeparators();
    file_permissions_.erase(stripped);
    request_file_set_.erase(stripped);
  }
