This is UI side unreadable device support.

chrome/browser/chromeos/cros/mount_library.cc

Index: chrome/browser/chromeos/cros/mount_library.cc
diff --git a/chrome/browser/chromeos/cros/mount_library.cc b/chrome/browser/chromeos/cros/mount_library.cc
index 4fd4c5c38b6ee08d47b5bd69194b786fb93a4ec9..090e58b3b6b239bd65d46debdde611c9b5dc0c09 100644
--- a/chrome/browser/chromeos/cros/mount_library.cc
+++ b/chrome/browser/chromeos/cros/mount_library.cc
@@ -173,7 +173,7 @@ class MountLibraryImpl : public MountLibrary {
     CHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
     if (!CrosLibrary::Get()->EnsureLoaded()) {
       OnMountCompleted(MOUNT_ERROR_LIBRARY_NOT_LOADED,
-                       MountPointInfo(source_path, NULL, type));
+                       MountPointInfo(source_path, NULL, type, NULL));
       return;
     }
     libcros_proxy_->CallMountPath(source_path, type, options,
@@ -330,9 +330,20 @@ class MountLibraryImpl : public MountLibrary {
                                     MountType type,
                                     const char* mount_path) {
     DCHECK(object);
+    std::string special_data;
+    if (type == MOUNT_TYPE_DEVICE) {
+      if (error_code == MOUNT_ERROR_UNKNOWN_FILESYSTEM)
+          special_data = "unreadable_unknown_filesystem";
+      if (error_code == MOUNT_ERROR_UNSUPORTED_FILESYSTEM)
+          special_data = "unreadable_unsupported_filesystem";
+    }
+
     MountLibraryImpl* self = static_cast<MountLibraryImpl*>(object);
     self->OnMountCompleted(static_cast<MountError>(error_code),
-                           MountPointInfo(source_path, mount_path, type));
+                           MountPointInfo(source_path,
+                                          mount_path,
+                                          type,
+                                          special_data.c_str()));
   }
 
   // Callback for UnmountRemovableDevice method.
@@ -435,14 +446,17 @@ class MountLibraryImpl : public MountLibrary {
 
     FireMountCompleted(MOUNTING, error_code, mount_info);
 
-    if (error_code == MOUNT_ERROR_NONE &&
+    // If the device is corrupted but it's still possible to format it, it will
+    // be fake mounted.
+
+    if ((error_code == MOUNT_ERROR_NONE || !mount_info.special_data.empty()) &&
         mount_points_.find(mount_info.mount_path) == mount_points_.end()) {
       mount_points_.insert(MountPointMap::value_type(
                                mount_info.mount_path.c_str(),
                                mount_info));
     }
 
-    if (error_code == MOUNT_ERROR_NONE &&
+    if ((error_code == MOUNT_ERROR_NONE || !mount_info.special_data.empty()) &&
         mount_info.mount_type == MOUNT_TYPE_DEVICE &&
         !mount_info.source_path.empty() &&
         !mount_info.mount_path.empty()) {
@@ -472,7 +486,8 @@ class MountLibraryImpl : public MountLibrary {
           MOUNT_ERROR_NONE,
           MountPointInfo(mount_points_it->second.source_path.c_str(),
                          mount_points_it->second.mount_path.c_str(),
-                         mount_points_it->second.mount_type));
+                         mount_points_it->second.mount_type,
+                         mount_points_it->second.special_data.c_str()));
       std::string path(mount_points_it->second.source_path);
       mount_points_.erase(mount_points_it);
       DiskMap::iterator iter = disks_.find(path);