Use size_t more consistently for packet/payload lengths.

See design doc at https://docs.google.com/a/chromium.org/document/d/1I6nmE9D_BmCY-IoV6MDPY2V6WYpEI-dg2apWXTfZyUI/edit?usp=sharing for more information.

This CL was reviewed and approved in pieces in the following CLs:
https://webrtc-codereview.appspot.com/24209004/
https://webrtc-codereview.appspot.com/24229004/
https://webrtc-codereview.appspot.com/24259004/
https://webrtc-codereview.appspot.com/25109004/
https://webrtc-codereview.appspot.com/26099004/
https://webrtc-codereview.appspot.com/27069004/
https://webrtc-codereview.appspot.com/27969004/
https://webrtc-codereview.appspot.com/27989004/
https://webrtc-codereview.appspot.com/29009004/
https://webrtc-codereview.appspot.com/30929004/
https://webrtc-codereview.appspot.com/30939004/
https://webrtc-codereview.appspot.com/31999004/
Committing as TBR to the original reviewers.

BUG=chromium:81439
TEST=none
TBR=pthatcher,henrik.lundin,tina.legrand,stefan,tkchin,glaznev,kjellander,perkj,mflodman,henrika,asapersson,niklas.enbom

Review URL: https://webrtc-codereview.appspot.com/23129004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7726 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/webrtc/system_wrappers/interface/file_wrapper.h b/webrtc/system_wrappers/interface/file_wrapper.h
index 68dc005..a618634 100644
--- a/webrtc/system_wrappers/interface/file_wrapper.h
+++ b/webrtc/system_wrappers/interface/file_wrapper.h
@@ -69,12 +69,12 @@
   // Inherited from Instream.
   // Reads |length| bytes from file to |buf|. Returns the number of bytes read
   // or -1 on error.
-  virtual int Read(void* buf, int length) = 0;
+  virtual int Read(void* buf, size_t length) = 0;
 
   // Inherited from OutStream.
   // Writes |length| bytes from |buf| to file. The actual writing may happen
   // some time later. Call Flush() to force a write.
-  virtual bool Write(const void* buf, int length) = 0;
+  virtual bool Write(const void* buf, size_t length) = 0;
 
   // Inherited from both Instream and OutStream.
   // Rewinds the file to the start. Only available when OpenFile() has been