Fixed bookkeeping bug in management of dimensions of mailbox's texture.

Source/platform/graphics/gpu/DrawingBuffer.cpp

Index: Source/platform/graphics/gpu/DrawingBuffer.cpp
diff --git a/Source/platform/graphics/gpu/DrawingBuffer.cpp b/Source/platform/graphics/gpu/DrawingBuffer.cpp
index 91cca8137b8389850c3a51f76506a0a97d757e73..9edcb4ee4d9284f7ad4195bb3b7cfd3672839fef 100644
--- a/Source/platform/graphics/gpu/DrawingBuffer.cpp
+++ b/Source/platform/graphics/gpu/DrawingBuffer.cpp
@@ -501,7 +501,7 @@ bool DrawingBuffer::resizeFramebuffer(const IntSize& size)
     m_context->bindTexture(GraphicsContext3D::TEXTURE_2D, m_colorBuffer);
     m_context->texImage2DResourceSafe(GraphicsContext3D::TEXTURE_2D, 0, m_internalColorFormat, size.width(), size.height(), 0, m_colorFormat, GraphicsContext3D::UNSIGNED_BYTE);
     if (m_lastColorBuffer)
-        m_lastColorBuffer->size = m_size;
+        m_lastColorBuffer->size = size;
 
     m_context->framebufferTexture2D(GraphicsContext3D::FRAMEBUFFER, GraphicsContext3D::COLOR_ATTACHMENT0, GraphicsContext3D::TEXTURE_2D, m_colorBuffer, 0);