Adds support for reading and writing 10/12-bit y4m

The y4m extension used is the same as the one used in ffmpeg/x264.
The patch is adapted from the highbitdepth branch.

Also adds unit tests for y4m header parsing and md5 check
of the raw frame data, as well as y4m writing.

Change-Id: Ie2794daf6dbafd2f128464f9b9da520fc54c0dd6

test/y4m_video_source.h

diff --git a/test/y4m_video_source.h b/test/y4m_video_source.h
index 7419043..378e75b 100644
--- a/test/y4m_video_source.h
+++ b/test/y4m_video_source.h
@@ -38,24 +38,30 @@
     CloseSource();
   }
 
-  virtual void Begin() {
+  virtual void OpenSource() {
     CloseSource();
     input_file_ = OpenTestDataFile(file_name_);
     ASSERT_TRUE(input_file_ != NULL) << "Input file open failed. Filename: "
-        << file_name_;
+                                     << file_name_;
+  }
 
-    y4m_input_open(&y4m_, input_file_, NULL, 0, 0);
+  virtual void ReadSourceToStart() {
+    ASSERT_TRUE(input_file_ != NULL);
+    ASSERT_FALSE(y4m_input_open(&y4m_, input_file_, NULL, 0, 0));
     framerate_numerator_ = y4m_.fps_n;
     framerate_denominator_ = y4m_.fps_d;
-
     frame_ = 0;
     for (unsigned int i = 0; i < start_; i++) {
-        Next();
+      Next();
     }
-
     FillFrame();
   }
 
+  virtual void Begin() {
+    OpenSource();
+    ReadSourceToStart();
+  }
+
   virtual void Next() {
     ++frame_;
     FillFrame();