Fix crash when reading from a isolated file system which is unmounted.

Previously, the underlying code was assuming that creating file stream readers
always succeeds (DCHECK), however it's not the case for isolated file systems
which are removed gracefully.

TEST=See bug repro steps.
BUG=477488

Review URL: https://codereview.chromium.org/1131323003

Cr-Commit-Position: refs/heads/master@{#331112}

2 files changed, 55 insertions, 26 deletions

diff --git a/storage/browser/blob/blob_url_request_job.cc b/storage/browser/blob/blob_url_request_job.cc
index 4362706..513c1a8 100644
--- a/storage/browser/blob/blob_url_request_job.cc
+++ b/storage/browser/blob/blob_url_request_job.cc
@@ -197,7 +197,7 @@ bool BlobURLRequestJob::AddItemLength(size_t index, int64 item_length) {
   return true;
 }
 
-void BlobURLRequestJob::CountSize() {
+bool BlobURLRequestJob::CountSize() {
   TRACE_EVENT_ASYNC_BEGIN1("Blob", "BlobRequest::CountSize", this, "uuid",
                            blob_data_->uuid());
   pending_get_file_info_count_ = 0;
@@ -209,18 +209,28 @@ void BlobURLRequestJob::CountSize() {
     const BlobDataItem& item = *items.at(i);
     if (IsFileType(item.type())) {
       ++pending_get_file_info_count_;
-      GetFileStreamReader(i)->GetLength(
-          base::Bind(&BlobURLRequestJob::DidGetFileItemLength,
-                     weak_factory_.GetWeakPtr(), i));
+      storage::FileStreamReader* const reader = GetFileStreamReader(i);
+      if (!reader) {
+        NotifyFailure(net::ERR_FAILED);
+        return false;
+      }
+      if (!reader->GetLength(
+              base::Bind(&BlobURLRequestJob::DidGetFileItemLength,
+                         weak_factory_.GetWeakPtr(), i))) {
+        NotifyFailure(net::ERR_FILE_NOT_FOUND);
+        return false;
+      }
       continue;
     }
 
     if (!AddItemLength(i, item.length()))
-      return;
+      return false;
   }
 
   if (pending_get_file_info_count_ == 0)
     DidCountSize(net::OK);
+
+  return true;
 }
 
 void BlobURLRequestJob::DidCountSize(int error) {
@@ -346,12 +356,18 @@ bool BlobURLRequestJob::ReadItem() {
   const BlobDataItem& item = *items.at(current_item_index_);
   if (item.type() == DataElement::TYPE_BYTES)
     return ReadBytesItem(item, bytes_to_read);
-  if (IsFileType(item.type())) {
-    return ReadFileItem(GetFileStreamReader(current_item_index_),
-                        bytes_to_read);
+  if (!IsFileType(item.type())) {
+    NOTREACHED();
+    return false;
   }
-  NOTREACHED();
-  return false;
+  storage::FileStreamReader* const reader =
+      GetFileStreamReader(current_item_index_);
+  if (!reader) {
+    NotifyFailure(net::ERR_FAILED);
+    return false;
+  }
+
+  return ReadFileItem(reader, bytes_to_read);
 }
 
 void BlobURLRequestJob::AdvanceItem() {
@@ -576,14 +592,16 @@ FileStreamReader* BlobURLRequestJob::GetFileStreamReader(size_t index) {
   DCHECK_LT(index, items.size());
   const BlobDataItem& item = *items.at(index);
   if (!IsFileType(item.type()))
-    return NULL;
-  if (index_to_reader_.find(index) == index_to_reader_.end())
-    CreateFileStreamReader(index, 0);
+    return nullptr;
+  if (index_to_reader_.find(index) == index_to_reader_.end()) {
+    if (!CreateFileStreamReader(index, 0))
+      return nullptr;
+  }
   DCHECK(index_to_reader_[index]);
   return index_to_reader_[index];
 }
 
-void BlobURLRequestJob::CreateFileStreamReader(size_t index,
+bool BlobURLRequestJob::CreateFileStreamReader(size_t index,
                                                int64 additional_offset) {
   const auto& items = blob_data_->items();
   DCHECK_LT(index, items.size());
@@ -591,15 +609,16 @@ void BlobURLRequestJob::CreateFileStreamReader(size_t index,
   DCHECK(IsFileType(item.type()));
   DCHECK_EQ(0U, index_to_reader_.count(index));
 
-  FileStreamReader* reader = NULL;
+  FileStreamReader* reader = nullptr;
   switch (item.type()) {
     case DataElement::TYPE_FILE:
       reader = FileStreamReader::CreateForLocalFile(
-          file_task_runner_.get(),
-          item.path(),
-          item.offset() + additional_offset,
-          item.expected_modification_time());
-      break;
+          file_task_runner_.get(), item.path(),
+          item.offset() + additional_offset, item.expected_modification_time());
+      DCHECK(reader);
+      index_to_reader_[index] = reader;
+      return true;
+
     case DataElement::TYPE_FILE_FILESYSTEM:
       reader = file_system_context_
                    ->CreateFileStreamReader(
@@ -611,12 +630,21 @@ void BlobURLRequestJob::CreateFileStreamReader(size_t index,
                              : item.length() - additional_offset,
                          item.expected_modification_time())
                    .release();
-      break;
+      if (reader) {
+        index_to_reader_[index] = reader;
+        return true;
+      }
+
+      // The file stream reader may not be obtainable if the file is on an
+      // isolated file system, which has been unmounted.
+      return false;
+
     default:
-      NOTREACHED();
+      break;
   }
-  DCHECK(reader);
-  index_to_reader_[index] = reader;
+
+  NOTREACHED();
+  return false;
 }
 
 }  // namespace storage
diff --git a/storage/browser/blob/blob_url_request_job.h b/storage/browser/blob/blob_url_request_job.h
index b9c3040..a4e10ed 100644
--- a/storage/browser/blob/blob_url_request_job.h
+++ b/storage/browser/blob/blob_url_request_job.h
@@ -60,7 +60,7 @@ class STORAGE_EXPORT BlobURLRequestJob
   // For preparing for read: get the size, apply the range and perform seek.
   void DidStart();
   bool AddItemLength(size_t index, int64 item_length);
-  void CountSize();
+  bool CountSize();
   void DidCountSize(int error);
   void DidGetFileItemLength(size_t index, int64 result);
   void Seek(int64 offset);
@@ -90,7 +90,8 @@ class STORAGE_EXPORT BlobURLRequestJob
   FileStreamReader* GetFileStreamReader(size_t index);
 
   // Creates a FileStreamReader for the item at |index| with additional_offset.
-  void CreateFileStreamReader(size_t index, int64 additional_offset);
+  // If failed, then returns false.
+  bool CreateFileStreamReader(size_t index, int64 additional_offset);
 
   scoped_ptr<BlobDataSnapshot> blob_data_;