arc: Support non-standard display scale factors.

ui/gfx/image/image_skia.cc

Index: ui/gfx/image/image_skia.cc
diff --git a/ui/gfx/image/image_skia.cc b/ui/gfx/image/image_skia.cc
index 20349b4baf14c71cd7fd7200697b559abc4fcf84..9c4ef646ecac6af3b4e0bd1ca98911e7b67b621e 100644
--- a/ui/gfx/image/image_skia.cc
+++ b/ui/gfx/image/image_skia.cc
@@ -219,18 +219,8 @@ std::vector<ImageSkiaRep>::iterator ImageSkiaStorage::FindRepresentation(
 
     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);
@@ -331,6 +321,15 @@ float ImageSkia::GetMaxSupportedScale() {
 }
 
 // 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));
 }