Adding null pointer check in BaseRenderingContext2D::restoreMatrixClipStack

third_party/WebKit/Source/modules/canvas2d/BaseRenderingContext2D.cpp

 // Copyright 2016 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 "modules/canvas2d/BaseRenderingContext2D.h"
 
 #include "bindings/core/v8/ExceptionMessages.h"
 #include "bindings/core/v8/ExceptionState.h"
 #include "bindings/core/v8/ExceptionStatePlaceholder.h"
 #include "core/css/cssom/CSSURLImageValue.h"
@@ skipping 80 matching lines @@
   validateStateStack();
 }
 
 void BaseRenderingContext2D::restoreMatrixClipStack(SkCanvas* c) const {
   if (!c)
     return;
   HeapVector<Member<CanvasRenderingContext2DState>>::const_iterator currState;
   DCHECK(m_stateStack.begin() < m_stateStack.end());
   for (currState = m_stateStack.begin(); currState < m_stateStack.end();
        currState++) {
-    CHECK(currState->get());
     c->setMatrix(SkMatrix::I());
-    currState->get()->playbackClips(c);
-    c->setMatrix(affineTransformToSkMatrix(currState->get()->transform()));
+    if (currState->get()) {
+      currState->get()->playbackClips(c);
+      c->setMatrix(affineTransformToSkMatrix(currState->get()->transform()));
+    }
     c->save();
   }
   c->restore();
   validateStateStack();
 }
 
 void BaseRenderingContext2D::unwindStateStack() {
   if (size_t stackSize = m_stateStack.size()) {
     if (SkCanvas* skCanvas = existingDrawingCanvas()) {
       while (--stackSize)
@@ skipping 1898 matching lines @@
       ExpensiveCanvasHeuristicParameters::ShadowFixedCost[index] *
           m_usageCounters.numBlurredShadows +
       ExpensiveCanvasHeuristicParameters::
               ShadowVariableCostPerAreaTimesShadowBlurSquared[index] *
           m_usageCounters.boundingBoxAreaTimesShadowBlurSquared;
 
   return basicCostOfDrawCalls + fillTypeAdjustment + shadowAdjustment;
 }
 
 }  // namespace blink