Initial support for cloudprint in print preview

printing/printing.gyp

Index: printing/printing.gyp
diff --git a/printing/printing.gyp b/printing/printing.gyp
index 38371453d12cdd915d9d4bd23f9a02e244211315..4e657d771d53424b6d34f6081babf3df5e0a59ee 100644
--- a/printing/printing.gyp
+++ b/printing/printing.gyp
@@ -146,6 +146,16 @@
             'backend/print_backend_cups.cc',
           ],
         }],
+        ['OS=="linux" and chromeos==1', {
+          'defines': [
+            # PRINT_BACKEND_AVAILABLE disables the default dummy implementation
+            # of the print backend and enables a custom implementation instead.
+            'PRINT_BACKEND_AVAILABLE',
+          ],
+          'sources': [
+            'backend/print_backend_chromeos.cc',
+          ],
+        }],
       ],
     },
     {