Add FileReaderInterface::ReadExactly() and FileSeekerInterface::SeekSet()

util/file/file_seeker.cc

Index: util/file/file_seeker.cc
diff --git a/util/file/file_seeker.cc b/util/file/file_seeker.cc
new file mode 100644
index 0000000000000000000000000000000000000000..a38e2f918546e955a1e114215907c35f3820a230
--- /dev/null
+++ b/util/file/file_seeker.cc
@@ -0,0 +1,37 @@
+// Copyright 2015 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "util/file/file_seeker.h"
+
+#include "base/logging.h"
+
+namespace crashpad {
+
+FileOffset FileSeekerInterface::SeekGet() {
+  return Seek(0, SEEK_CUR);
+}
+
+bool FileSeekerInterface::SeekSet(FileOffset offset) {
+  FileOffset rv = Seek(offset, SEEK_SET);
+  if (rv < 0) {
+    // Seek() will have logged its own error.
+    return false;
+  } else if (rv != offset) {
+    LOG(ERROR) << "SeekSet(): expected " << offset << ", observed " << rv;
+    return false;
+  }
+  return true;
+}
+
+}  // namespace crashpad