[battor agent] Don't log all bytes received when reading sample frames

tools/battor_agent/battor_connection_impl.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "tools/battor_agent/battor_connection_impl.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
 #include "base/memory/ptr_util.h"
@@ skipping 210 matching lines @@
   }
 
   if (bytes_read == 0) {
     // If we didn't have a message before, and we weren't able to read any
     // additional bytes, then there's no valid message available.
     LogSerial("Read failed due to no bytes being read.");
     EndReadBytes(false, BATTOR_MESSAGE_TYPE_CONTROL, nullptr);
     return;
   }
 
-  LogSerial(StringPrintf(
-      "%d more bytes read: %s.", bytes_read,
-      CharArrayToString(pending_read_buffer_->data(), bytes_read).c_str()));
+  if (pending_read_message_type_ == BATTOR_MESSAGE_TYPE_SAMPLES) {
+    // If we're reading samples, don't log every byte that we receive. This
+    // exacerbates a problem on Mac wherein we can't process sample frames
+    // quickly enough to prevent the serial buffer from overflowing, causing us
+    // to drop frames.
+    LogSerial(StringPrintf("%d more bytes read.", bytes_read));
+  } else {
+    LogSerial(StringPrintf(
+        "%d more bytes read: %s.", bytes_read,
+        CharArrayToString(pending_read_buffer_->data(), bytes_read).c_str()));
+  }
 
   already_read_buffer_.insert(already_read_buffer_.end(),
                               pending_read_buffer_->data(),
                               pending_read_buffer_->data() + bytes_read);
 
   BattOrMessageType type;
   size_t message_max_bytes =
       GetMaxBytesForMessageType(pending_read_message_type_);
   std::unique_ptr<vector<char>> bytes(new vector<char>());
   bytes->reserve(message_max_bytes);
@@ skipping 100 matching lines @@
   base::ThreadTaskRunnerHandle::Get()->PostTask(
       FROM_HERE,
       base::Bind(&Listener::OnBytesSent, base::Unretained(listener_), success));
 }
 
 void BattOrConnectionImpl::LogSerial(const std::string& str) {
   serial_log_ << str << std::endl << std::endl;
 }
 
 }  // namespace battor