Add a manifest property declaring USB printers supported by an app.

extensions/common/api/extensions_manifest_types.json

Index: extensions/common/api/extensions_manifest_types.json
diff --git a/extensions/common/api/extensions_manifest_types.json b/extensions/common/api/extensions_manifest_types.json
index 1829174ae7b25e9c1f0b64f103bbbb65efb08cb3..266039836e04969cab37821ebdaefe1561145013 100644
--- a/extensions/common/api/extensions_manifest_types.json
+++ b/extensions/common/api/extensions_manifest_types.json
@@ -162,6 +162,46 @@
             "optional": true
           }
         }
+      },
+      {
+        "id": "UsbPrinters",
+        "type": "object",
+        "description": "The <code>usb_printers</code> manifest property lists the USB printers supported by an app implementing the $(ref:printerProvider) API.",
+        "properties": {
+          "filters": {
+            "description": "A list of $(ref:usb.DeviceFilter USB device filters) matching supported devices. A device only needs to match one of the provided filters. A <code>vendorId</code> is required and only one of <code>productId</code> or <code>interfaceClass</code> may be provided.",
+            "type": "array",
+            "items": {
+              "type": "object",
+              "properties": {
+                "vendorId": {
+                  "description": "USB vendor ID of matching devices",
+                  "type": "integer"
+                },
+                "productId": {
+                  "description": "USB product ID of matching devices",
+                  "type": "integer",
+                  "optional": true
+                },
+                "interfaceClass": {
+                  "description": "USB interface class implemented by any interface of a matching device.",
+                  "type": "integer",
+                  "optional": true
+                },
+                "interfaceSubclass": {
+                  "description": "USB interface sub-class implemented by the interface matching $(ref:interfaceClass).",
+                  "type": "integer",
+                  "optional": true
+                },
+                "interfaceProtocol": {
+                  "description": "USB interface protocol implemented by the interface matching $(ref:interfaceClass) and $(ref:interfaceProtocol).",
+                  "type": "integer",
+                  "optional": true

[asargent_no_longer_on_chrome, 2015/05/07 18:13:43]

In the usb API documentation, for interfaceSubclass and interfaceProtocol we
mention that these are only checked if interfaceClass and interfaceSubclass,
respectively, are provided. Would it make sense to mention the same thing here? 

[Reilly Grant (use Gerrit), 2015/05/07 20:33:25]

That was my intention in referencing interfaceClass and interfaceSubclass here
(except I mentioned interfaceProtocol instead).

+                }
+              }
+            }
+          }
+        }
       }
     ]
   }