Use file handles to interact with utility process.

chrome/common/chrome_utility_printing_messages.h

Index: chrome/common/chrome_utility_printing_messages.h
diff --git a/chrome/common/chrome_utility_printing_messages.h b/chrome/common/chrome_utility_printing_messages.h
index d0a964d895685c85bda68661e1ed197109e27d53..8bdf7b07e1ba3b0ea5eb73058c2fd653bbb34f22 100644
--- a/chrome/common/chrome_utility_printing_messages.h
+++ b/chrome/common/chrome_utility_printing_messages.h
@@ -121,20 +121,21 @@ IPC_MESSAGE_CONTROL1(
 
 #if defined(OS_WIN)
 // Tell the utility process to render the given PDF into a metafile.
-// The metafile path will have ".%d" inserted where the %d is the page number.
-// If no page range is specified, all pages will be converted.
-IPC_MESSAGE_CONTROL4(ChromeUtilityMsg_RenderPDFPagesToMetafiles,
-                     IPC::PlatformFileForTransit,  // PDF file
-                     base::FilePath,  // Base location for output metafile
-                     printing::PdfRenderSettings,  // PDF render settings
-                     std::vector<printing::PageRange>)
-
-// Reply when the utility process has succeeded in rendering the PDF.
-IPC_MESSAGE_CONTROL2(ChromeUtilityHostMsg_RenderPDFPagesToMetafiles_Succeeded,
-                     std::vector<printing::PageRange>,  // Pages rendered
-                     double)                            // Scale factor
-
-// Reply when an error occurred rendering the PDF.
-IPC_MESSAGE_CONTROL0(ChromeUtilityHostMsg_RenderPDFPagesToMetafile_Failed)
-
+IPC_MESSAGE_CONTROL2(ChromeUtilityMsg_RenderPDFPagesToMetafiles,

[Lei Zhang, 2014/09/15 21:49:53]

BTW, this should go in the "Utility process messages" section between lines
60-86.

[Vitaly Buka (NO REVIEWS), 2014/09/15 22:33:50]

Done.

+                     IPC::PlatformFileForTransit, /* input_file */
+                     printing::PdfRenderSettings /* settings */)
+
+// Reply when the utility process has succeeded in rendering the PDF page.
+IPC_MESSAGE_CONTROL1(ChromeUtilityHostMsg_RenderPDFPagesToMetafiles_PageCount,
+                     int /* page_count */)
+
+// Requests conversion of the next page.
+IPC_MESSAGE_CONTROL2(ChromeUtilityHostMsg_RenderPDFPagesToMetafiles_GetPage,

[Lei Zhang, 2014/09/15 21:49:53]

This should be a ChromeUtilityMsg and go in the above section.

[Vitaly Buka (NO REVIEWS), 2014/09/15 22:33:50]

Done.

+                     int /* page_number */,
+                     IPC::PlatformFileForTransit /* output_file */)
+
+// Reply when the utility process has succeeded in rendering the PDF page.
+IPC_MESSAGE_CONTROL2(ChromeUtilityHostMsg_RenderPDFPagesToMetafiles_PageDone,
+                     bool /* success */,
+                     double /* scale_factor */)
 #endif  // OS_WIN