arc: Support non-standard display scale factors.

ui/gfx/image/image_skia.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/image/image_skia.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <cmath>
@@ skipping 201 matching lines @@
       smallest_diff = diff;
     }
   }
 
   if (fetch_new_image && source_.get()) {
     DCHECK(CalledOnValidThread())
         << "An ImageSkia with the source must be accessed by the same thread.";
 
     ImageSkiaRep image;
     float resource_scale = scale;
-    if (!HasRepresentationAtAllScales() && g_supported_scales) {
-      if (g_supported_scales->back() <= scale) {
-        resource_scale = g_supported_scales->back();
-      } else {
-        for (size_t i = 0; i < g_supported_scales->size(); ++i) {
-          if ((*g_supported_scales)[i] + kFallbackToSmallerScaleDiff >= scale) {
-            resource_scale = (*g_supported_scales)[i];
-            break;
-          }
-        }
-      }
-    }
+    if (!HasRepresentationAtAllScales() && g_supported_scales)
+      resource_scale = ImageSkia::MapToSupportedScale(scale);
     if (scale != resource_scale) {
       std::vector<ImageSkiaRep>::iterator iter =
           FindRepresentation(resource_scale, fetch_new_image);
       CHECK(iter != image_reps_.end());
       image = iter->unscaled() ? (*iter) : ScaleImageSkiaRep(*iter, scale);
     } else {
       image = source_->GetImageForScale(scale);
       // Image may be missing for the specified scale in some cases, such like
       // looking up 2x resources but the 2x resource pack is missing. Fall back
       // to 1x and re-scale it.
@@ skipping 80 matching lines @@
   DCHECK(g_supported_scales != NULL);
   return *g_supported_scales;
 }
 
 // static
 float ImageSkia::GetMaxSupportedScale() {
   return g_supported_scales->back();
 }
 
 // static
+float ImageSkia::MapToSupportedScale(float scale) {
+  for (float supported_scale : *g_supported_scales) {
+    if (supported_scale + kFallbackToSmallerScaleDiff >= scale)
+      return supported_scale;
+  }
+  return g_supported_scales->back();
+}
+
+// static
 ImageSkia ImageSkia::CreateFrom1xBitmap(const SkBitmap& bitmap) {
   return ImageSkia(ImageSkiaRep(bitmap, 0.0f));
 }
 
 std::unique_ptr<ImageSkia> ImageSkia::DeepCopy() const {
   ImageSkia* copy = new ImageSkia;
   if (isNull())
     return base::WrapUnique(copy);
 
   CHECK(CanRead());
@@ skipping 174 matching lines @@
 bool ImageSkia::CanModify() const {
   return !storage_.get() || storage_->CanModify();
 }
 
 void ImageSkia::DetachStorageFromThread() {
   if (storage_.get())
     storage_->DetachFromThread();
 }
 
 }  // namespace gfx