Use DPI from Print Preview on Windows, handle non square

printing/print_job_constants.cc

Index: printing/print_job_constants.cc
diff --git a/printing/print_job_constants.cc b/printing/print_job_constants.cc
index a613d8e0aff04c104c5b8ec1bb3c3d78ed31f6c1..c0b4935e865a14d4f108cd905d8369d9ffd061bc 100644
--- a/printing/print_job_constants.cc
+++ b/printing/print_job_constants.cc
@@ -56,6 +56,12 @@ const char kSettingDeviceName[] = "deviceName";
 // Option to disable scaling. True if scaling is disabled else false.
 const char kSettingDisableScaling[] = "disableScaling";
 
+// Horizontal DPI
+const char kSettingDpiHorizontal[] = "dpiHorizontal";
+
+// Vertical DPI
+const char kSettingDpiVertical[] = "dpiVertical";
+
 // Scaling value required to fit the document to page.
 const char kSettingFitToPageScaling[] = "fitToPageScaling";