Bug 1144392 - Show an error message in the Browser Toolbox if the connection fails. r=jryans

browser/devtools/framework/toolbox-process-window.js

@@ -62,7 +62,13 @@ window.addEventListener("load", function() {
   let cmdClose = document.getElementById("toolbox-cmd-close");
   cmdClose.addEventListener("command", onCloseCommand);
   setPrefDefaults();
-  connect().catch(Cu.reportError);
+  connect().catch(e => {
+    let errorMessageContainer = document.getElementById("error-message-container");
+    let errorMessage = document.getElementById("error-message");
+    errorMessage.value = e;
+    errorMessageContainer.hidden = false;
+    Cu.reportError(e);
+  });
 });
 
 function onCloseCommand(event) {

browser/devtools/framework/toolbox-process-window.xul

@@ -37,5 +37,9 @@
        for example when viewing network request details. -->
   <popupset id="mainPopupSet"></popupset>
 
+  <vbox id="error-message-container" hidden="true" flex="1">
+    <box>&browserToolboxErrorMessage;</box>
+    <textbox multiline="true" id="error-message" flex="1"></textbox>
+  </vbox>
   <iframe id="toolbox-iframe" flex="1"></iframe>
 </window>

browser/locales/en-US/chrome/browser/devtools/toolbox.dtd

@@ -23,6 +23,10 @@
   -  It allows you to switch the context of the whole toolbox. -->
 <!ENTITY toolboxFramesTooltip          "Select an iframe as the currently targeted document">
 
+<!-- LOCALIZATION NOTE (browserToolboxErrorMessage): This is the label
+  -  shown next to error details when the Browser Toolbox is unable to open. -->
+<!ENTITY browserToolboxErrorMessage          "Error opening Browser Toolbox:">
+
 <!-- LOCALIZATION NOTE (options.context.advancedSettings): This is the label for
   -  the heading of the advanced settings group in the options panel. -->
 <!ENTITY options.context.advancedSettings "Advanced settings">