Use a correct scale factor in app_list::CachedLabel

It currently just uses 1.0. Instead, fetch it with
ui::GetScaleFactorForNativeView and invalidate it when the scale factor
changes.

This is a small fix for a simple HiDPI bug, but eventually we will be
able to scrap CachedLabel: The performance improvement it offers will be
redundant with http://crbug.com/240037.

BUG=368493

Review URL: https://codereview.chromium.org/405373002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@284649 0039d316-1c4b-4281-b951-d872f2087c98

ui/app_list/views/cached_label.cc

@@ -5,8 +5,10 @@
 #include "ui/app_list/views/cached_label.h"
 
 #include "base/strings/utf_string_conversions.h"
+#include "ui/base/layout.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/gfx/canvas.h"
+#include "ui/views/widget/widget.h"
 
 namespace app_list {
 
@@ -19,7 +21,9 @@ void CachedLabel::PaintToBackingImage() {
     return;
 
   bool is_opaque = SkColorGetA(background_color()) == 0xFF;
-  gfx::Canvas canvas(size(), 1.0f, is_opaque);
+  float scale_factor =
+      ui::GetScaleFactorForNativeView(GetWidget()->GetNativeView());
+  gfx::Canvas canvas(size(), scale_factor, is_opaque);
   // If a background is provided, it will initialize the canvas in
   // View::OnPaintBackground(). Otherwise, the background must be set here.
   if (!background()) {
@@ -38,4 +42,10 @@ void CachedLabel::OnPaint(gfx::Canvas* canvas) {
 }
 #endif
 
+void CachedLabel::OnDeviceScaleFactorChanged(
+    float device_scale_factor) {
+  Invalidate();
+  View::OnDeviceScaleFactorChanged(device_scale_factor);
+}
+
 }  // namespace app_list

ui/app_list/views/cached_label.h

@@ -27,10 +27,13 @@ class CachedLabel : public views::Label {
   void PaintToBackingImage();
 
 #if defined(OS_WIN)
-  // views::View overrides.
+  // Overridden from views::View:
   virtual void OnPaint(gfx::Canvas* canvas) OVERRIDE;
 #endif
 
+  // Overridden from ui::LayerDelegate:
+  virtual void OnDeviceScaleFactorChanged(float device_scale_factor) OVERRIDE;
+
  private:
   bool needs_repaint_;
   gfx::ImageSkia image_;