Fix assert in m_stack.isEmpty() in GraphicsContext::~GraphicsContext()

Save and restore is not balanced in GraphicsContext. This causes
the log error "ERROR void GraphicsContext::restore() stack is empty"
and assert in the GraphicsContext destructor.

The cause is a mismatch of GraphicsContexts being saved and restored by
TextureMapperImageBuffer beginClip and endClip. This patch fixes endClip
to restore the currentContext beginClip saved.

Change-Id: Ief0100dd26c7eded04734167e86712a81f1a7674
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>

2 files changed, 10 insertions, 1 deletions

diff --git a/Source/WebCore/platform/graphics/texmap/TextureMapperImageBuffer.cpp b/Source/WebCore/platform/graphics/texmap/TextureMapperImageBuffer.cpp
index c04e576db..668ea95b1 100644
--- a/Source/WebCore/platform/graphics/texmap/TextureMapperImageBuffer.cpp
+++ b/Source/WebCore/platform/graphics/texmap/TextureMapperImageBuffer.cpp
@@ -114,6 +114,15 @@ void TextureMapperImageBuffer::beginClip(const TransformationMatrix& matrix, con
 #endif
 }
 
+void TextureMapperImageBuffer::endClip()
+{
+    GraphicsContext* context = currentContext();
+    if (!context)
+        return;
+
+    context->restore();
+}
+
 void TextureMapperImageBuffer::drawTexture(const BitmapTexture& texture, const FloatRect& targetRect, const TransformationMatrix& matrix, float opacity, unsigned /* exposedEdges */)
 {
     GraphicsContext* context = currentContext();
diff --git a/Source/WebCore/platform/graphics/texmap/TextureMapperImageBuffer.h b/Source/WebCore/platform/graphics/texmap/TextureMapperImageBuffer.h
index 060713ce5..637d9d33b 100644
--- a/Source/WebCore/platform/graphics/texmap/TextureMapperImageBuffer.h
+++ b/Source/WebCore/platform/graphics/texmap/TextureMapperImageBuffer.h
@@ -59,7 +59,7 @@ public:
     virtual void drawSolidColor(const FloatRect&, const TransformationMatrix&, const Color&) OVERRIDE;
     virtual void beginClip(const TransformationMatrix&, const FloatRect&) OVERRIDE;
     virtual void bindSurface(BitmapTexture* surface) OVERRIDE { m_currentSurface = surface;}
-    virtual void endClip() OVERRIDE { graphicsContext()->restore(); }
+    virtual void endClip() OVERRIDE;
     virtual IntRect clipBounds() OVERRIDE { return currentContext()->clipBounds(); }
     virtual IntSize maxTextureSize() const;
     virtual PassRefPtr<BitmapTexture> createTexture() OVERRIDE { return BitmapTextureImageBuffer::create(); }