Optionally clear PlatformCanvas instances.

skia/ext/platform_canvas_unittest.cc

 // Copyright (c) 2006-2008 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.
 
 // TODO(awalker): clean up the const/non-const reference handling in this test
 
 #include "build/build_config.h"
 
 #if defined(OS_MACOSX)
 #import <ApplicationServices/ApplicationServices.h>
@@ skipping 134 matching lines @@
   LayerSaver(PlatformCanvas& canvas, int x, int y, int w, int h)
       : canvas_(canvas),
         x_(x),
         y_(y),
         w_(w),
         h_(h) {
     SkRect bounds;
     bounds.set(SkIntToScalar(x_), SkIntToScalar(y_),
                SkIntToScalar(right()), SkIntToScalar(bottom()));
     canvas_.saveLayer(&bounds, NULL);
+    canvas.clear(SkColorSetARGB(0, 0, 0, 0));
   }
 
   ~LayerSaver() {
     canvas_.restore();
   }
 
   int x() const { return x_; }
   int y() const { return y_; }
   int w() const { return w_; }
   int h() const { return h_; }
@@ skipping 215 matching lines @@
     MakeOpaque(&canvas, kLayerX, kLayerY, kLayerW, kLayerH);
 #endif
   }
   canvas.restore();
   EXPECT_TRUE(VerifyRoundedRect(canvas, SK_ColorWHITE, SK_ColorBLACK,
                                 kInnerX + 1, kInnerY + 1, kInnerW, kInnerH));
 #endif
 }
 
 }  // namespace skia