Print preview: Use an ID instead of memory pointer string in WebUI.

BUG=144051

Review URL: https://chromiumcodereview.appspot.com/10870003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@153342 0039d316-1c4b-4281-b951-d872f2087c98
  void VerifyPrintPreviewInvalidPrinterSettings(bool settings_invalid) {
    bool print_preview_invalid_printer_settings =
        (render_thread_->sink().GetUniqueMessageMatching(
            PrintHostMsg_PrintPreviewInvalidPrinterSettings::ID) != NULL);
    EXPECT_EQ(settings_invalid, print_preview_invalid_printer_settings);
  }

  void VerifyPrintPreviewInvalidPrinterSettings(bool settings_invalid) {
    bool print_preview_invalid_printer_settings =
        (render_thread_->sink().GetUniqueMessageMatching(
            PrintHostMsg_PrintPreviewInvalidPrinterSettings::ID) != NULL);
    EXPECT_EQ(settings_invalid, print_preview_invalid_printer_settings);
  }
