Update UI and catch executeScript errors now shown in Canary

go-back-with-backspace/background.js

Index: go-back-with-backspace/background.js
diff --git a/go-back-with-backspace/background.js b/go-back-with-backspace/background.js
index 269b0bdf0f4b35b53cf3b4ed4db9f9d04e10ecc2..9c715aa7782731a5dad8edc25980b8a9af3c3678 100644
--- a/go-back-with-backspace/background.js
+++ b/go-back-with-backspace/background.js
@@ -29,14 +29,27 @@ function injectContentScripts() {
   chrome.tabs.query({}, function(tabs) {
     tabs.forEach(function(tab) {
       scripts.forEach(function(script) {
-        // This will produce an error if extensions are prohibited on the
-        // tab (e.g., chrome:// pages), but we can ignore it.
-        chrome.tabs.executeScript(tab.id,
-                                  {
-                                    file: script,
-                                    allFrames: true,
-                                    runAt: 'document_start'
-                                  });
+        chrome.tabs.executeScript(
+          tab.id,
+          {
+            file: script,
+            allFrames: true,
+            runAt: 'document_start'
+          },
+          function() {
+            if (chrome.runtime.lastError) {
+              // An error will occur if extensions are prohibited on the
+              // tab (e.g., chrome:// pages). We don't need to do anything
+              // about that, but we do need to catch it here to avoid an
+              // error message on the Extensions page.
+              var message = chrome.runtime.lastError.message;
+              if (message != 'Cannot access a chrome:// URL' &&
+                  message != 'The extensions gallery cannot be scripted.' &&
+                  !message.startsWith('Cannot access contents of the page.')) {
+                throw message;
+              }
+            }
+          });
       });
     });
   });