Add tracing for ContentLayerDelegate paintContents and DisplayItemList commit.

Source/platform/graphics/ContentLayerDelegate.cpp

Index: Source/platform/graphics/ContentLayerDelegate.cpp
diff --git a/Source/platform/graphics/ContentLayerDelegate.cpp b/Source/platform/graphics/ContentLayerDelegate.cpp
index d817f1fcc0709207a2f379dfdccbc64f5ad13ccc..11645f6453c4d82fe74b748430d9fd2325dce1bd 100644
--- a/Source/platform/graphics/ContentLayerDelegate.cpp
+++ b/Source/platform/graphics/ContentLayerDelegate.cpp
@@ -28,6 +28,8 @@
 
 #include "platform/EventTracer.h"
 #include "platform/RuntimeEnabledFeatures.h"
+#include "platform/TraceEvent.h"
+#include "platform/TracedValue.h"
 #include "platform/geometry/IntRect.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/paint/DisplayItemList.h"
@@ -51,10 +53,24 @@ ContentLayerDelegate::~ContentLayerDelegate()
 {
 }
 
+PassRefPtr<TracedValue> toTracedValue(const WebRect& clip)
+{
+    RefPtr<TracedValue> tracedValue = TracedValue::create();
+    tracedValue->beginArray();
+    tracedValue->pushInteger(clip.x);
+    tracedValue->pushInteger(clip.y);
+    tracedValue->pushInteger(clip.x + clip.width);
+    tracedValue->pushInteger(clip.y + clip.height);

[Xianzhu, 2015/06/23 22:58:54]

The third and fourth values of rect might be ambiguous to readers. It seems that
we use width and height (e.g. GraphicsLayerDebugInfo and rectAsJSONArray in
GraphicsLayer.cpp) more than maxX, maxY in blink. Better to keep the
consistency.

[chrishtr, 2015/06/23 23:05:38]

Done.

+    tracedValue->endArray();
+    return tracedValue;
+}
+
 void ContentLayerDelegate::paintContents(
     SkCanvas* canvas, const WebRect& clip,
     WebContentLayerClient::PaintingControlSetting paintingControl)
 {
+    TRACE_EVENT1("blink,benchmark", "ContentLayerDelegate::paintContents", "clip_rect", toTracedValue(clip));
+
     ASSERT(!RuntimeEnabledFeatures::slimmingPaintEnabled());
 
     GraphicsContext::DisabledMode disabledMode = GraphicsContext::NothingDisabled;
@@ -70,6 +86,8 @@ void ContentLayerDelegate::paintContents(
     WebDisplayItemList* webDisplayItemList, const WebRect& clip,
     WebContentLayerClient::PaintingControlSetting paintingControl)
 {
+    TRACE_EVENT1("blink,benchmark", "ContentLayerDelegate::paintContents", "clip_rect", toTracedValue(clip));
+
     ASSERT(RuntimeEnabledFeatures::slimmingPaintEnabled());
 
     DisplayItemList* displayItemList = m_painter->displayItemList();