simplify scrollcanvas to always use shared code

ui/gfx/blit.cc

 // Copyright (c) 2012 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 "ui/gfx/blit.h"
 
 #include <stddef.h>
 
 #include "base/logging.h"
 #include "build/build_config.h"
@@ skipping 53 matching lines @@
 
   return false;
 }
 
 }  // namespace
 
 void ScrollCanvas(SkCanvas* canvas,
                   const gfx::Rect& in_clip,
                   const gfx::Vector2d& offset) {
   DCHECK(!HasClipOrTransform(*canvas));  // Don't support special stuff.
-#if defined(OS_WIN)
-  // If we have a PlatformCanvas, we should use ScrollDC. Otherwise, fall
-  // through to the software implementation.
-  if (skia::SupportsPlatformPaint(canvas)) {
-    skia::ScopedPlatformPaint scoped_platform_paint(canvas);
-    HDC hdc = scoped_platform_paint.GetNativeDrawingContext();
 
-    RECT damaged_rect;
-    RECT r = in_clip.ToRECT();
-    ScrollDC(hdc, offset.x(), offset.y(), NULL, &r, NULL, &damaged_rect);
-    return;
-  }
-#endif  // defined(OS_WIN)
-  // For non-windows, always do scrolling in software.
-  // Cairo has no nice scroll function so we do our own. On Mac it's possible to
-  // use platform scroll code, but it's complex so we just use the same path
-  // here. Either way it will be software-only, so it shouldn't matter much.
   SkPixmap pixmap;
-  skia::GetWritablePixels(canvas, &pixmap);
+  bool success = skia::GetWritablePixels(canvas, &pixmap);
+  DCHECK(success);
 
   // We expect all coords to be inside the canvas, so clip here.
   gfx::Rect clip = gfx::IntersectRects(
       in_clip, gfx::Rect(0, 0, pixmap.width(), pixmap.height()));
 
   // Compute the set of pixels we'll actually end up painting.
   gfx::Rect dest_rect = gfx::IntersectRects(clip + offset, clip);
   if (dest_rect.size().IsEmpty())
     return;  // Nothing to do.
 
@@ skipping 21 matching lines @@
     // Fortunately, memmove already handles this for us.
     for (int y = 0; y < dest_rect.height(); y++) {
       memmove(pixmap.writable_addr32(dest_rect.x(), dest_rect.y() + y),
               pixmap.addr32(src_rect.x(), src_rect.y() + y),
               row_bytes);
     }
   }
 }
 
 }  // namespace gfx