remove legacy code from PlatformCanvas days

According to the comment, this extra copy was needed when the bitmaps in a platform-canvas
wasn't ref-countable. That is no longer the case (hasn't been true for quite a while AFAIK)
so this CL removes that code.

BUG=

Review-Url: https://codereview.chromium.org/2799283003
Cr-Commit-Position: refs/heads/master@{#462845}

chrome/browser/thumbnails/content_based_thumbnailing_algorithm.cc

@@ -133,19 +133,6 @@ SkBitmap ContentBasedThumbnailingAlgorithm::PrepareSourceBitmap(
 
   SkBitmap result_bitmap = SkBitmapOperations::DownsampleByTwoUntilSize(
       clipped_bitmap, resize_target.width(), resize_target.height());
-#if !defined(USE_AURA)
-  // If the bitmap has not been indeed resized, it has to be copied. In that
-  // case resampler simply returns a reference to the original bitmap, sitting
-  // in PlatformCanvas. One does not simply assign these 'magic' bitmaps to
-  // SkBitmap. They cannot be refcounted.
-  //
-  // With Aura, this does not happen since PlatformCanvas is platform
-  // idependent.
-  if (clipped_bitmap.width() == result_bitmap.width() &&
-      clipped_bitmap.height() == result_bitmap.height()) {
-    clipped_bitmap.copyTo(&result_bitmap, kN32_SkColorType);
-  }
-#endif
 
   return result_bitmap;
 }

chrome/browser/thumbnails/simple_thumbnail_crop.cc

@@ -177,24 +177,6 @@ SkBitmap SimpleThumbnailCrop::CreateThumbnail(const SkBitmap& bitmap,
   // close, and let the caller make it the exact size if desired.
   SkBitmap result = SkBitmapOperations::DownsampleByTwoUntilSize(
       clipped_bitmap, desired_size.width(), desired_size.height());
-#if !defined(USE_AURA)
-  // This is a bit subtle. SkBitmaps are refcounted, but the magic
-  // ones in PlatformCanvas can't be assigned to SkBitmap with proper
-  // refcounting.  If the bitmap doesn't change, then the downsampler
-  // will return the input bitmap, which will be the reference to the
-  // weird PlatformCanvas one insetad of a regular one. To get a
-  // regular refcounted bitmap, we need to copy it.
-  //
-  // On Aura, the PlatformCanvas is platform-independent and does not have
-  // any native platform resources that can't be refounted, so this issue does
-  // not occur.
-  //
-  // Note that GetClippedBitmap() does extractSubset() but it won't copy
-  // the pixels, hence we check result size == clipped_bitmap size here.
-  if (clipped_bitmap.width() == result.width() &&
-      clipped_bitmap.height() == result.height())
-    clipped_bitmap.copyTo(&result, kN32_SkColorType);
-#endif
 
   LOCAL_HISTOGRAM_TIMES(kThumbnailHistogramName,
                         base::TimeTicks::Now() - begin_compute_thumbnail);