Consider trigger intermediate report in ProxyFlow

[cloudendpoints]

Consider trigger intermediate report in ProxyFlow

[qiwzhang]

It is good idea, we can use both byte based and time elapse based criteria to trigger a intermediate report.

for example:

if ((read_bytes > T || write_bytes > T) && (time_elapse > 1s))

[chowchow316]

The code hook-up is tricky: if we want to remove timer, the intermediate report will be triggered in proxy_flow.cc, which is inside api_manger/grpc, the code structure will become complex. To optimize the performance with timer, we can set a byte threshold (1MB) to trigger the report, and extend the timer period (1s -> 10s).

[lizan]

No, it won't be tricky, the only tricky part is grpc is currently setting up as a content handler (not a filter)

You should add a IntermediateReport() into RequestHandlerInterface, and call it from grpc_server_call.cc. When we move grpc/transcoding to filter, then IntermediateReport() can be called in filter. All condition check should live in IntermediateReport().

[chowchow316]

Added #27 to get rid of timer.