Add histogram for IIRFilter orders

third_party/WebKit/Source/modules/webaudio/IIRFilterNode.cpp

Index: third_party/WebKit/Source/modules/webaudio/IIRFilterNode.cpp
diff --git a/third_party/WebKit/Source/modules/webaudio/IIRFilterNode.cpp b/third_party/WebKit/Source/modules/webaudio/IIRFilterNode.cpp
index 0cf20480324d354b2f7beddd9f74b94e074f3051..d00ee260d097aee1ac56cb39821c2aec4d28155b 100644
--- a/third_party/WebKit/Source/modules/webaudio/IIRFilterNode.cpp
+++ b/third_party/WebKit/Source/modules/webaudio/IIRFilterNode.cpp
@@ -8,6 +8,7 @@
 #include "bindings/core/v8/ExceptionState.h"
 #include "core/dom/ExceptionCode.h"
 #include "modules/webaudio/AudioBasicProcessorHandler.h"
+#include "platform/Histogram.h"
 
 namespace blink {
 
@@ -17,6 +18,14 @@ IIRFilterNode::IIRFilterNode(AbstractAudioContext& context, float sampleRate, co
     setHandler(AudioBasicProcessorHandler::create(
         AudioHandler::NodeTypeIIRFilter, *this, sampleRate,
         adoptPtr(new IIRProcessor(sampleRate, 1, feedforwardCoef, feedbackCoef))));
+
+    // Histogram of the IIRFilter order.  createIIRFilter ensures that the length of |feedbackCoef|
+    // is in the range [1, IIRFilter::kMaxOrder + 1].  The order is one less than the length of this
+    // vector.
+    DEFINE_STATIC_LOCAL(CustomCountHistogram, qHistogram,

[hongchan, 2016/04/28 22:07:07]

Why qHistogram? Does |q| have some meaning?

[Raymond Toy, 2016/04/28 22:09:17]

Don't know. I stole this example from the blink thread on this.

[jbroman, 2016/04/28 22:18:09]

nit: "qHistogram" was a name in my example because it was "Q" that was being
recorded. Suggest a name that describes what this records ("orderHistogram"?).

[Raymond Toy, 2016/04/28 22:44:12]

Renamed to filterOrderHistogram.

+        ("WebAudio.IIRFilterNode.order", 0, IIRFilter::kMaxOrder, IIRFilter::kMaxOrder + 1));

[jbroman, 2016/04/28 22:18:09]

CustomCountHistogram is, by default, logarithmic; here I think you want a linear
histogram. I believe EnumerationHistogram is intended for cases like this:

DEFINE_STATIC_LOCAL(EnumerationHistogram, orderHistogram,
    ("WebAudio.IIRFilterNode.Order", IIRFilter::kMaxOrder + 1));
orderHistogram.count(feedbackCoef.size() - 1);

[Raymond Toy, 2016/04/28 22:44:12]

Changed to EnumerationHistogram. (It's impossible to figure out what these
things mean from reading platform/Histogram.h.)

+
+    qHistogram.count(feedbackCoef.size() - 1);
 }
 
 DEFINE_TRACE(IIRFilterNode)