Revert of Delete VideoFrame default constructor, and IsZeroSize method.

webrtc/common_video/i420_video_frame_unittest.cc

Index: webrtc/common_video/i420_video_frame_unittest.cc
diff --git a/webrtc/common_video/i420_video_frame_unittest.cc b/webrtc/common_video/i420_video_frame_unittest.cc
index 49cc4654fb34f7299404408300dc1edce4f0ae6a..62d14b9f4ac87851e7830a4078ced02febe20fd6 100644
--- a/webrtc/common_video/i420_video_frame_unittest.cc
+++ b/webrtc/common_video/i420_video_frame_unittest.cc
@@ -111,6 +111,12 @@
 
 }  // namespace
 
+TEST(TestVideoFrame, InitialValues) {
+  VideoFrame frame;
+  EXPECT_TRUE(frame.IsZeroSize());
+  EXPECT_EQ(kVideoRotation_0, frame.rotation());
+}
+
 TEST(TestVideoFrame, WidthHeightValues) {
   VideoFrame frame(I420Buffer::Create(10, 10, 10, 14, 90),
                    webrtc::kVideoRotation_0,