Assert on BeginPlatformPaint/EndPlatformPaint mismatch.

skia/ext/bitmap_platform_device_win.cc

Index: skia/ext/bitmap_platform_device_win.cc
===================================================================
--- skia/ext/bitmap_platform_device_win.cc	(revision 84213)
+++ skia/ext/bitmap_platform_device_win.cc	(working copy)
@@ -177,6 +177,7 @@
     : PlatformDevice(bitmap),
       data_(data) {
   // The data object is already ref'ed for us by create().
+  SkDEBUGCODE(begin_paint_count_ = 0);
 }
 
 // The copy constructor just adds another reference to the underlying data.
@@ -188,9 +189,11 @@
           const_cast<BitmapPlatformDevice&>(other).accessBitmap(true)),
       data_(other.data_) {
   data_->ref();
+  SkDEBUGCODE(begin_paint_count_ = 0);
 }
 
 BitmapPlatformDevice::~BitmapPlatformDevice() {
+  SkASSERT(begin_paint_count_ == 0);
   data_->unref();
 }
 
@@ -202,9 +205,15 @@
 }
 
 HDC BitmapPlatformDevice::BeginPlatformPaint() {
+  SkDEBUGCODE(begin_paint_count_++);
   return data_->GetBitmapDC();
 }
 
+void BitmapPlatformDevice::EndPlatformPaint() {
+  SkASSERT(begin_paint_count_--);
+  PlatformDevice::EndPlatformPaint();
+}
+
 void BitmapPlatformDevice::setMatrixClip(const SkMatrix& transform,
                                          const SkRegion& region,
                                          const SkClipStack&) {