Adds UMA histograms for WebRTC.DataChannelMaxRetransmits WebRTC.DataChannelMaxRetransmitTime.

content/renderer/media/rtc_data_channel_handler.cc

Index: content/renderer/media/rtc_data_channel_handler.cc
diff --git a/content/renderer/media/rtc_data_channel_handler.cc b/content/renderer/media/rtc_data_channel_handler.cc
index 9d2b56cba46d30c4379953d8cd1e5959f27f39a4..1fe4de11756a956473c13aff43f2cb24db18da95 100644
--- a/content/renderer/media/rtc_data_channel_handler.cc
+++ b/content/renderer/media/rtc_data_channel_handler.cc
@@ -4,6 +4,7 @@
 
 #include "content/renderer/media/rtc_data_channel_handler.h"
 
+#include <limits>
 #include <string>
 
 #include "base/logging.h"
@@ -45,6 +46,13 @@ RtcDataChannelHandler::RtcDataChannelHandler(
     IncrementCounter(CHANNEL_ORDERED);
   if (negotiated())
     IncrementCounter(CHANNEL_NEGOTIATED);
+
+  UMA_HISTOGRAM_CUSTOM_COUNTS("WebRTC.DataChannelMaxRetransmits",
+                              maxRetransmits(), 0,
+                              std::numeric_limits<unsigned short>::max(), 50);

[Ilya Sherman, 2014/05/08 00:27:02]

That's a mighty large upper bound.  Do you really expect the full range to be
used?

[perkj_chrome, 2014/05/08 13:59:45]

Both of these values are unsigned shorts that can be specified during
configurations from JS. So these are simply histograms of what the user has set.


std::numeric_limits<unsigned short>::max() has been used as not defined in the
code. 

[Ilya Sherman, 2014/05/09 00:18:51]

Yes, I see that.  However, all histograms have overflow buckets, so you don't
need to have your last non-overflow bucket be so large if you don't think it's
likely that users will actually use such large values.  OTOH, I guess it doesn't
really hurt; so if you prefer to keep things as they are, then LGTM.

+  UMA_HISTOGRAM_CUSTOM_COUNTS("WebRTC.DataChannelMaxRetransmitTime",
+                              maxRetransmitTime(), 0,
+                              std::numeric_limits<unsigned short>::max(), 50);

[Ilya Sherman, 2014/05/08 00:27:02]

Hmm, did you consider using one of the UMA_HISTOGRAM_TIMES macros?  Though, I
guess the max value you have set is only about a minute.  That still strikes me
as high for a networking time value, but maybe it's plausible here?

[perkj_chrome, 2014/05/08 13:59:45]

dito, see explanation above.

 }
 
 RtcDataChannelHandler::~RtcDataChannelHandler() {