Fix memory leak in GraphicsContextState.

Source/platform/graphics/GraphicsContextState.cpp

 // Copyright (c) 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "platform/graphics/GraphicsContextState.h"
 
 #include "platform/graphics/skia/SkiaUtils.h"
 
 namespace WebCore {
@@ skipping 41 matching lines @@
     , m_compositeOperator(other.m_compositeOperator)
     , m_blendMode(other.m_blendMode)
     , m_interpolationQuality(other.m_interpolationQuality)
     , m_saveCount(0)
     , m_shouldAntialias(other.m_shouldAntialias)
     , m_shouldSmoothFonts(other.m_shouldSmoothFonts)
     , m_shouldClampToSourceRect(other.m_shouldClampToSourceRect) { }
 
 void GraphicsContextState::copy(const GraphicsContextState& source)
 {
+    this->~GraphicsContextState();

[jbroman, 2014/06/12 13:43:07]

Wouldn't it be more straightforward to just make this a member-wise copy (like
an ordinary operator= implementation) rather than destructing and reconstructing
it? I wouldn't expect that to be any slower.

From a simplicity perspective, it would be even nicer to destruct objects as we
stop using them (and so avoid leaking their references to shaders and whatnot
until a sufficiently deep state stack occurs again). That's the default
behaviour of a Vector, so I assume that we decided this was a net performance
win.

[Dominik Grewe, 2014/06/12 13:50:19]

We mainly did this to avoid code duplication. But I'm happy to change it back to
simple assignments.
I agree, it would be nicer. Not sure why we're doing it but, as you said, maybe
we decided it was faster this way.

     new (this) GraphicsContextState(source);
 }
 
 const SkPaint& GraphicsContextState::strokePaint(int strokedPathLength) const
 {
     if (m_strokeData.gradient() && m_strokeData.gradient()->shaderChanged())
         m_strokePaint.setShader(m_strokeData.gradient()->shader());
     m_strokeData.setupPaintDashPathEffect(&m_strokePaint, strokedPathLength);
     return m_strokePaint;
 }
@@ skipping 174 matching lines @@
 
 void GraphicsContextState::setShouldAntialias(bool shouldAntialias)
 {
     m_shouldAntialias = shouldAntialias;
     m_strokePaint.setAntiAlias(shouldAntialias);
     m_fillPaint.setAntiAlias(shouldAntialias);
 }
 
 
 } // namespace WebCore