Add printing.dll to the component build.

printing/pdf_metafile_cg_mac.h

Index: printing/pdf_metafile_cg_mac.h
===================================================================
--- printing/pdf_metafile_cg_mac.h	(revision 98598)
+++ printing/pdf_metafile_cg_mac.h	(working copy)
@@ -25,7 +25,7 @@
 namespace printing {
 
 // This class creates a graphics context that renders into a PDF data stream.
-class PdfMetafileCg : public Metafile, public base::ThreadChecker {
+class PRINTING_EXPORT PdfMetafileCg : public Metafile {
  public:
   PdfMetafileCg();
   virtual ~PdfMetafileCg();
@@ -69,6 +69,8 @@
   // Returns a CGPDFDocumentRef version of pdf_data_.
   CGPDFDocumentRef GetPDFDocument() const;
 
+  base::ThreadChecker thread_checker_;
+
   // Context for rendering to the pdf.
   base::mac::ScopedCFTypeRef<CGContextRef> context_;