Trace contention for lockPixels mutex

src/core/SkPixelRef.cpp

Index: src/core/SkPixelRef.cpp
diff --git a/src/core/SkPixelRef.cpp b/src/core/SkPixelRef.cpp
index dea8c8aed0ce9daa0f3977f779082b2a37d58a3e..20a8b34f067ff7eafc35759cb96b1b94de475a56 100644
--- a/src/core/SkPixelRef.cpp
+++ b/src/core/SkPixelRef.cpp
@@ -8,6 +8,7 @@
 #include "SkBitmapCache.h"
 #include "SkPixelRef.h"
 #include "SkThread.h"
+#include "SkTraceEvent.h"
 
 #ifdef SK_BUILD_FOR_WIN32
     // We don't have SK_BASE_MUTEX_INIT on Windows.
@@ -155,7 +156,9 @@ bool SkPixelRef::lockPixels(LockRec* rec) {
     SkASSERT(!fPreLocked || SKPIXELREF_PRELOCKED_LOCKCOUNT == fLockCount);
 
     if (!fPreLocked) {
+        TRACE_EVENT_BEGIN0("skia", "SkPixelRef::lockPixelsMutex");
         SkAutoMutexAcquire  ac(*fMutex);
+        TRACE_EVENT_END0("skia", "SkPixelRef::lockPixelsMutex");
 
         if (1 == ++fLockCount) {
             SkASSERT(fRec.isZero());