Replace Check for too many pending frames in I420_buffer_pool with returning nullptr. Added histogr…

webrtc/common_video/i420_buffer_pool_unittest.cc

Index: webrtc/common_video/i420_buffer_pool_unittest.cc
diff --git a/webrtc/common_video/i420_buffer_pool_unittest.cc b/webrtc/common_video/i420_buffer_pool_unittest.cc
index d5c7c9bbd8c08905be43519dd9075f0da25d8161..a4dda0c60e8a70b5e5fac6b506658a0ededfb462 100644
--- a/webrtc/common_video/i420_buffer_pool_unittest.cc
+++ b/webrtc/common_video/i420_buffer_pool_unittest.cc
@@ -63,4 +63,11 @@ TEST(TestI420BufferPool, FrameValidAfterPoolDestruction) {
   memset(buffer->MutableDataY(), 0xA5, 16 * buffer->StrideY());
 }
 
+TEST(TestI420BufferPool, MaxNumberOfBuffers) {
+  I420BufferPool pool(false, 1);
+  rtc::scoped_refptr<VideoFrameBuffer> buffer1 = pool.CreateBuffer(16, 16);
+  EXPECT_NE(nullptr, buffer1.get());
+  EXPECT_EQ(nullptr, pool.CreateBuffer(16, 16).get());
+}
+
 }  // namespace webrtc