Add job id to JobEventDetails.

printing/printing_context.h

Index: printing/printing_context.h
diff --git a/printing/printing_context.h b/printing/printing_context.h
index 6335461b06d1f9c02c66900832388b7f91d7d79d..362dfe9ba6b2cf588fd02b3e9184431b7a91bbc4 100644
--- a/printing/printing_context.h
+++ b/printing/printing_context.h
@@ -125,6 +125,8 @@ class PRINTING_EXPORT PrintingContext {
     return settings_;
   }
 
+  int job_id() const { return job_id_; }
+
  protected:
   explicit PrintingContext(Delegate* delegate);
 
@@ -146,6 +148,9 @@ class PRINTING_EXPORT PrintingContext {
   // Did the user cancel the print job.
   volatile bool abort_printing_;
 
+  // The job id for the current job. The value is 0 if no jobs are active.
+  int job_id_;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(PrintingContext);
 };