Fix 2D canvas drawImage handling of non-invertible transform matrices

Source/core/html/canvas/CanvasRenderingContext2D.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008 Dirk Schulze <krit@webkit.org>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  * Copyright (C) 2012, 2013 Intel Corporation. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
@@ skipping 1264 matching lines @@
     SkCanvas* c = drawingCanvas();
     ASSERT(c);
 
     int initialSaveCount = c->getSaveCount();
     SkPaint imagePaint = *paint;
 
     if (paint->getImageFilter()) {
         SkMatrix ctm = c->getTotalMatrix();
         SkMatrix invCtm;
         if (!ctm.invert(&invCtm)) {
-            ASSERT_NOT_REACHED(); // There is an earlier check for invertibility
+            // There is an earlier check for invertibility, but the arithmetic
+            // in AffineTransform is not exactly identical, so it is possible
+            // for SkMatrix to find the transform to be non-invertible at this stage.
+            // crbug.com/504687
+            return;
         }
         c->save();
         c->concat(invCtm);
         SkRect bounds = dstRect;
         ctm.mapRect(&bounds);
         SkRect filteredBounds;
         paint->getImageFilter()->computeFastBounds(bounds, &filteredBounds);
         SkPaint layerPaint;
         layerPaint.setXfermode(paint->getXfermode());
         layerPaint.setImageFilter(paint->getImageFilter());
@@ skipping 939 matching lines @@
         if (imageType == CanvasRenderingContext2DState::NonOpaqueImage)
             return;
         if (alpha < 0xFF)
             return;
     }
 
     canvas()->buffer()->willOverwriteCanvas();
 }
 
 } // namespace blink