Download location: Fix an issue in file writing.

When we write to a file, currently we assume the whole chunk is written.
However when users pull out the SD card or disk, base::File::Write will
return a size less than the chunk size, and the next call to
base::File::Write will return an error.

This CL fixed this issue so FILE_FAILED error can be correctly reported
when the SD card is unmounted.

This CL basically makes the core write function back to this revision:
https://chromium.googlesource.com/chromium/src/+/29db19d0c973a8990283ec4b81111db5bdb8d2de/content/browser/download/base_file.cc#101

Bug: 841559,792775
Change-Id: Icfba65833bf3aec07d30d8d3bed57a9abba7f8d1
Reviewed-on: https://chromium-review.googlesource.com/1053233
Commit-Queue: Xing Liu <xingliu@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557903}

components/download/internal/common/base_file.cc

@@ -13,6 +13,7 @@
 #include "base/format_macros.h"
 #include "base/logging.h"
 #include "base/macros.h"
+#include "base/numerics/safe_conversions.h"
 #include "base/pickle.h"
 #include "base/strings/stringprintf.h"
 #include "base/threading/thread_restrictions.h"
@@ -137,22 +138,35 @@ DownloadInterruptReason BaseFile::WriteDataToFile(int64_t offset,
   // belong to the same download will be grouped together.
   CONDITIONAL_TRACE(
       NESTABLE_ASYNC_BEGIN0("download", "DownloadFileWrite", download_id_));
-  int write_result = file_.Write(offset, data, data_len);
+
+  if (bytes_so_far_ != offset) {
+    // A hole is created in the file.
+    is_sparse_file_ = true;
+    secure_hash_.reset();
+  }
+
+  // Writes to the file.
+  int64_t len = base::saturated_cast<int64_t>(data_len);
+  const char* current_data = data;
+  int64_t current_offset = offset;
+  while (len > 0) {
+    // |write_result| may be less than |len|, and return an error on the next
+    // write call when the disk is unavaliable.
+    int write_result = file_.Write(current_offset, current_data, len);
     DCHECK_NE(0, write_result);
 
     // Report errors on file writes.
     if (write_result < 0)
       return LogSystemError("Write", logging::GetLastSystemErrorCode());
 
-  DCHECK_EQ(static_cast<size_t>(write_result), data_len);
-
-  if (bytes_so_far_ != offset) {
-    // A hole is created in the file.
-    is_sparse_file_ = true;
-    secure_hash_.reset();
+    // Update status.
+    DCHECK_LE(write_result, len);
+    len -= write_result;
+    current_data += write_result;
+    current_offset += write_result;
+    bytes_so_far_ += write_result;
   }
 
-  bytes_so_far_ += data_len;
   CONDITIONAL_TRACE(NESTABLE_ASYNC_END1("download", "DownloadFileWrite",
                                         download_id_, "bytes", data_len));