Revert of mojo filesystem: Simplify full file reading/writing.

components/filesystem/file_impl.cc

Index: components/filesystem/file_impl.cc
diff --git a/components/filesystem/file_impl.cc b/components/filesystem/file_impl.cc
index 8a3682b075e0c20bb1bc26b5edb4054be7b95877..da156c8618c7a3e0c5e378d8cf554dedec12e11f 100644
--- a/components/filesystem/file_impl.cc
+++ b/components/filesystem/file_impl.cc
@@ -92,6 +92,28 @@
   DCHECK_LE(static_cast<size_t>(num_bytes_read), num_bytes_to_read);
   bytes_read.resize(static_cast<size_t>(num_bytes_read));
   callback.Run(FileError::OK, std::move(bytes_read));
+}
+
+void FileImpl::ReadEntireFile(const ReadEntireFileCallback& callback) {
+  if (!file_.IsValid()) {
+    callback.Run(GetError(file_), mojo::Array<uint8_t>());
+    return;
+  }
+
+  // Seek to the front of the file.
+  if (file_.Seek(base::File::FROM_BEGIN, 0) == -1) {
+    callback.Run(FileError::FAILED, mojo::Array<uint8_t>());
+    return;
+  }
+
+  std::string contents;
+  const int kBufferSize = 1 << 16;
+  scoped_ptr<char[]> buf(new char[kBufferSize]);
+  size_t len;
+  while ((len = file_.ReadAtCurrentPos(buf.get(), kBufferSize)) > 0)
+    contents.append(buf.get(), len);
+
+  callback.Run(FileError::OK, mojo::Array<uint8_t>::From(contents));
 }
 
 // TODO(vtl): Move the implementation to a thread pool.