PrintPreview: Preview generation should not block print button.

chrome/browser/ui/webui/print_preview_ui.h

Index: chrome/browser/ui/webui/print_preview_ui.h
diff --git a/chrome/browser/ui/webui/print_preview_ui.h b/chrome/browser/ui/webui/print_preview_ui.h
index 58ceda8488c1960b7dc47cc77dbc7f1e9a3a17c8..95657610514e4d1ff2789ade98f3e27124cbf48b 100644
--- a/chrome/browser/ui/webui/print_preview_ui.h
+++ b/chrome/browser/ui/webui/print_preview_ui.h
@@ -44,6 +44,15 @@ class PrintPreviewUI : public ChromeWebUI {
   // message.
   void OnInitiatorTabClosed(const std::string& initiator_tab_url);
 
+  void setTabHiddenForPrint() {
+    is_tab_hidden_for_print_ = true;
+  }
+
+  // Returns true if the current tab is hidden for printing.
+  bool isHidden() {
+    return is_tab_hidden_for_print_;
+  }
+
  private:
   // Helper function
   PrintPreviewDataService* print_preview_data_service();
@@ -53,6 +62,9 @@ class PrintPreviewUI : public ChromeWebUI {
   // Store the PrintPreviewUI address string.
   std::string preview_ui_addr_str_;
 
+  // True when the current tab is hidden for printing.
+  bool is_tab_hidden_for_print_;
+
   DISALLOW_COPY_AND_ASSIGN(PrintPreviewUI);
 };