Handle EINTR and remove offset_t in ffmpeg code.

media/filters/ffmpeg_glue.cc

Index: media/filters/ffmpeg_glue.cc
diff --git a/media/filters/ffmpeg_glue.cc b/media/filters/ffmpeg_glue.cc
index a920f58a3471524bf4784bc12f941c8a6cb6f697..e35d96e9c0b1745f4e2392cd141cdee8cebd57c0 100644
--- a/media/filters/ffmpeg_glue.cc
+++ b/media/filters/ffmpeg_glue.cc
@@ -39,9 +39,9 @@ int WriteContext(URLContext* h, unsigned char* buf, int size) {
   return AVERROR_IO;
 }
 
-offset_t SeekContext(URLContext* h, offset_t offset, int whence) {
+int64 SeekContext(URLContext* h, int64 offset, int whence) {
   media::FFmpegURLProtocol* protocol = ToProtocol(h->priv_data);
-  offset_t new_offset = AVERROR_IO;
+  int64 new_offset = AVERROR_IO;
   switch (whence) {
     case SEEK_SET:
       if (protocol->SetPosition(offset))