Adding performance tracking for canvas API calls

third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp

Index: third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp b/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
index 5c8f2329b9f16f6332811ff126ce444d048ada06..e907301636b8fda1f9195eb31104c113416dbe63 100644
--- a/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
@@ -604,6 +604,18 @@ String HTMLCanvasElement::toDataURLInternal(const String& mimeType, const double
 
 String HTMLCanvasElement::toDataURL(const String& mimeType, const ScriptValue& qualityArgument, ExceptionState& exceptionState) const
 {
+    Optional<ScopedUsHistogramTimer> timer;
+    if (m_imageBuffer && m_imageBuffer->isAccelerated()) {
+        DEFINE_STATIC_LOCAL(CustomCountHistogram, scopedUsCounterGPU, ("Blink.Canvas.ToDataURL.GPU", 0, 10000000, 50));

[Justin Novosad, 2016/05/19 15:28:40]

You are missing entries in histograms.xml

+        timer.emplace(scopedUsCounterGPU);
+    } else if (m_imageBuffer && m_imageBuffer->isRecording()) {
+        DEFINE_STATIC_LOCAL(CustomCountHistogram, scopedUsCounterDL, ("Blink.Canvas.ToDataURL.DL", 0, 10000000, 50));

[Justin Novosad, 2016/05/19 15:28:39]

DL -> DisplayList

[xidachen, 2016/05/20 12:36:54]

Changed in all places.

+        timer.emplace(scopedUsCounterDL);
+    } else {
+        DEFINE_STATIC_LOCAL(CustomCountHistogram, scopedUsCounterSW, ("Blink.Canvas.ToDataURL.SW", 0, 10000000, 50));

[Justin Novosad, 2016/05/19 15:28:40]

SW -> CPU

[xidachen, 2016/05/20 12:36:54]

Changed in all places.

+        timer.emplace(scopedUsCounterSW);
+    }
+
     if (!originClean()) {
         exceptionState.throwSecurityError("Tainted canvases may not be exported.");

[Justin Novosad, 2016/05/19 15:36:55]

We should start the measurement after this early exit condition

[xidachen, 2016/05/20 12:36:54]

Done.

         return String();