Bug 1275707, part 3 - Rename MESSAGE_MANAGER_MESSAGE_SIZE. r=baku

Now that digits have been filtered out of the message manager message
names to avoid creating thousands of similar keys, we can reenable the
telemetry by renaming it. Also, update the description to address
bsmedberg's comments, and add me to the list of alert emails.

dom/base/nsFrameMessageManager.cpp

@@ -715,7 +715,7 @@ RecordMessageSize(size_t aDataLength, const nsAString& aMessageName)
   NS_ConvertUTF16toUTF8 messageName(aMessageName);
   messageName.StripChars("0123456789");
 
-  Telemetry::Accumulate(Telemetry::MESSAGE_MANAGER_MESSAGE_SIZE, messageName,
+  Telemetry::Accumulate(Telemetry::MESSAGE_MANAGER_MESSAGE_SIZE2, messageName,
                         aDataLength);
 }
 

toolkit/components/telemetry/Histograms.json

@@ -10749,15 +10749,16 @@
     "keyed": true,
     "description": "Measures the size of IPC messages by message name"
   },
-  "MESSAGE_MANAGER_MESSAGE_SIZE": {
-    "alert_emails": ["wmccloskey@mozilla.com"],
+  "MESSAGE_MANAGER_MESSAGE_SIZE2": {
+    "alert_emails": ["wmccloskey@mozilla.com","amccreight@mozilla.com"],
     "bug_numbers": [1260908],
     "expires_in_version": "55",
     "kind": "exponential",
+    "low": 8192,
     "high": 8000000,
     "n_buckets": 50,
     "keyed": true,
-    "description": "Measures the size of message manager messages by message name"
+    "description": "Each key is the message name, with digits removed, from an async message manager message that was larger than 8192 bytes, recorded in the sending process at the time of sending."
   },
   "SANDBOX_BROKER_INITIALIZED": {
     "alert_emails": ["bowen@mozilla.com"],