PrintPreview: Added code to identify the printer default duplex value.

printing/print_job_constants.h

Index: printing/print_job_constants.h
diff --git a/printing/print_job_constants.h b/printing/print_job_constants.h
index 76985991db9562befd56287ef1d60afe9e797389..47a3d000f4a906aba5b67cf2cc863ad6f8ee253f 100644
--- a/printing/print_job_constants.h
+++ b/printing/print_job_constants.h
@@ -10,6 +10,7 @@ namespace printing {
 extern const char kIsFirstRequest[];
 extern const char kPreviewRequestID[];
 extern const char kPreviewUIAddr[];
+extern const char kPrinterDefaultDuplexValue[];
 extern const char kSettingCloudPrintId[];
 extern const char kSettingCollate[];
 extern const char kSettingColor[];
@@ -18,7 +19,7 @@ extern const char kSettingContentWidth[];
 extern const char kSettingCopies[];
 extern const char kSettingDefaultMarginsSelected[];
 extern const char kSettingDeviceName[];
-extern const char kSettingDuplexMode[];
+extern const char kSettingDuplexModeInfo[];
 extern const char kSettingGenerateDraftData[];
 extern const char kSettingHeaderFooterEnabled[];
 extern const int kSettingHeaderFooterCharacterSpacing;
@@ -41,6 +42,7 @@ extern const char kSettingPageRangeFrom[];
 extern const char kSettingPageRangeTo[];
 extern const char kSettingPrinterName[];
 extern const char kSettingPrintToPDF[];
+extern const char kUserSelectedDuplexValue[];
 
 extern const int FIRST_PAGE_INDEX;
 extern const int COMPLETE_PREVIEW_DOCUMENT_INDEX;
@@ -52,6 +54,13 @@ enum DuplexMode {
   SHORT_EDGE,
 };
 
+// Specifies the possible default duplex setting values.
+enum DefaultDuplexSetting {
+  UNKNOWN = -1,
+  ONE_SIDED,
+  TWO_SIDED,
+};
+
 // Specifies the horizontal alignment of the headers and footers.
 enum HorizontalHeaderFooterPosition {
   LEFT,