Show a better error message for captureVisibleTab than just "internal error".

chrome/browser/extensions/api/tabs/tabs_api.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/extensions/api/tabs/tabs_api.h"
 
 #include <algorithm>
 #include <limits>
 #include <vector>
 
@@ skipping 1527 matching lines @@
   return true;
 }
 
 WebContents* TabsCaptureVisibleTabFunction::GetWebContentsForID(int window_id) {
   Browser* browser = NULL;
   if (!GetBrowserFromWindowID(&chrome_details_, window_id, &browser))
     return NULL;
 
   WebContents* contents = browser->tab_strip_model()->GetActiveWebContents();
   if (!contents) {
-    error_ = keys::kInternalVisibleTabCaptureError;
+    error_ = "No active web contents to capture";
     return NULL;
   }
 
   if (!extension()->permissions_data()->CanCaptureVisiblePage(
           SessionTabHelper::IdForTab(contents), &error_)) {
     return NULL;
   }
   return contents;
 }
 
 void TabsCaptureVisibleTabFunction::OnCaptureFailure(FailureReason reason) {
-  error_ = keys::kInternalVisibleTabCaptureError;
+  const char* reason_description = "internal error";
+  switch (reason) {
+    case FAILURE_REASON_UNKNOWN:
+      reason_description = "unknown error";
+      break;
+    case FAILURE_REASON_ENCODING_FAILED:
+      reason_description = "encoding failed";
+      break;
+    case FAILURE_REASON_VIEW_INVISIBLE:
+      reason_description = "view is invisible";
+      break;
+  }
+  error_ = ErrorUtils::FormatErrorMessage("Failed to capture tab: *",
+                                          reason_description);
   SendResponse(false);
 }
 
 void TabsCaptureVisibleTabFunction::RegisterProfilePrefs(
     user_prefs::PrefRegistrySyncable* registry) {
   registry->RegisterBooleanPref(
       prefs::kDisableScreenshots,
       false,
       user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
 }
@@ skipping 357 matching lines @@
   ZoomController::ZoomMode zoom_mode = zoom_controller->zoom_mode();
   api::tabs::ZoomSettings zoom_settings;
   ZoomModeToZoomSettings(zoom_mode, &zoom_settings);
 
   results_ = api::tabs::GetZoomSettings::Results::Create(zoom_settings);
   SendResponse(true);
   return true;
 }
 
 }  // namespace extensions