Add H.264 packetization.

This also includes:
- Creating new packetizer and depacketizer interfaces.
- Moved VP8 packetization was H264 packetization and depacketization to these interfaces. This is a work in progress and should be continued to get this 100% generic. This also required changing the return type for RtpFormatVp8::NextPacket(), which now returns bool instead of the index of the first partition.
- Created a Create() factory method for packetizers and depacketizers.

R=niklas.enbom@webrtc.org, pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/21009004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6804 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/video_coding/main/source/jitter_buffer.cc

@@ -482,7 +482,6 @@ bool VCMJitterBuffer::NextMaybeIncompleteTimestamp(uint32_t* timestamp) {
 
 VCMEncodedFrame* VCMJitterBuffer::ExtractAndSetDecode(uint32_t timestamp) {
   CriticalSectionScoped cs(crit_sect_);
-
   if (!running_) {
     return NULL;
   }
@@ -611,7 +610,6 @@ VCMFrameBufferEnum VCMJitterBuffer::InsertPacket(const VCMPacket& packet,
   if (error != kNoError && frame == NULL) {
     return error;
   }
-
   int64_t now_ms = clock_->TimeInMilliseconds();
   // We are keeping track of the first and latest seq numbers, and
   // the number of wraps to be able to calculate how many packets we expect.