Improve subscription error handling

Signed-off-by: Zoltan Kis 

Author: zolkis

index.html

@@ -1478,7 +1478,7 @@ The observeProperty() method
             Otherwise resolve |promise|.
           li>
           <li>
-            Whenever the underlying platform receives a notification for this
+            Whenever the underlying platform detects a notification for this
             subscription with a new <a>Propertya> value |value|,
             run the following sub-steps:
             <ul>
@@ -1493,15 +1493,19 @@ The observeProperty() method
             ul>
           li>
           <li>
-            Whenever the underlying platform receives an error notification for
-            this subscription with an |error:Error|, run the following sub-steps:
+            Whenever the underlying platform detects an error for
+            this subscription, run the following sub-steps:
             <ul>
               <li>
                 If the error is irrecoverable and stops the subscription, set
                 |subscription|'s |active| to `false` and suppress further notifications.
               li>
               <li>
-                If |onerror| is a {{Function}}, invoke it with |error|.
+                Let |error| be a new {{NetworkError}} and set its |message|
+                to reflect the underlying error condition.
+              li>
+              <li>
+                If |onerror| is a {{Function}},  invoke it with |error|.
               li>
             ul>
           li>
@@ -1625,7 +1629,7 @@ The subscribeEvent() method
             Otherwise resolve |promise|.
           li>
           <li>
-            Whenever the underlying platform receives a notification for this
+            Whenever the underlying platform detects a notification for this
             <a>Eventa> subscription, run the following sub-steps:
             <ol>
               <li>
@@ -1636,13 +1640,17 @@ The subscribeEvent() method
             ol>
           li>
           <li>
-            Whenever the underlying platform receives an error notification for
-            this subscription with an |error:Error|, run the following sub-steps:
+            Whenever the underlying platform detects an error for
+            this subscription, run the following sub-steps:
             <ul>
               <li>
                 If the error is irrecoverable and stops the subscription, set
                 |subscription|'s |active| to `false` and suppress further notifications.
               li>
+              <li>
+                Let |error| be a new {{NetworkError}} and set its |message|
+                to reflect the underlying error condition.
+              li>
               <li>
                 If |onerror| is a {{Function}}, invoke it with |error|.
               li>