vp8: Add missing call to SetUsageMessage().

Without it vp8_coder --help does not work.

BUG=None
TEST=ninja -C out/Debug && out/Debug/vp8_coder --help now shows the
usage message.

R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/44649005

Patch from Thiago Farina <tfarina@chromium.org>.

Cr-Commit-Position: refs/heads/master@{#8783}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8783 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/video_coding/codecs/vp8/vp8_sequence_coder.cc

@@ -211,6 +211,7 @@ int main(int argc, char** argv) {
 
   // Init the parser and set the usage message.
   parser.Init(argc, argv);
+  parser.SetUsageMessage(usage);
 
   // Reset flags.
   parser.SetFlag("w", "352");
@@ -224,6 +225,7 @@ int main(int argc, char** argv) {
                  webrtc::test::OutputPath() + "vp8_encoded.vp8");
   parser.SetFlag("input_file", webrtc::test::ResourcePath("foreman_cif",
                                                           "yuv"));
+  parser.SetFlag("help", "false");
 
   parser.ProcessFlags();
   if (parser.GetFlag("help") == "true") {