Print Preview: Hook up the print button to initiate printing without displaying a print dialog.

printing/printing_context.h

Index: printing/printing_context.h
diff --git a/printing/printing_context.h b/printing/printing_context.h
index 6d51f0209c3de41c931378c37ec49f1d61118603..2f109423e3a038298028dc6c02d5bbde71707f12 100644
--- a/printing/printing_context.h
+++ b/printing/printing_context.h
@@ -50,6 +50,10 @@ class PrintingContext {
   // Initializes with predefined settings.
   virtual Result InitWithSettings(const PrintSettings& settings) = 0;
 
+  // Update print settings. |job_settings| is a json string.
+  virtual Result UpdatePrintSettings(const std::string& job_settings,
+                                     const PageRanges& ranges) = 0;
+
   // Does platform specific setup of the printer before the printing. Signal the
   // printer that a document is about to be spooled.
   // Warning: This function enters a message loop. That may cause side effects