Load 2x resources on demand

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 65f2d48741233911458e18986c57f6ea12c4d56c..1816921a38814b8859a5708daedf6ba368903f0a 100644
--- a/ui/gfx/image/image_skia.cc
+++ b/ui/gfx/image/image_skia.cc
@@ -10,6 +10,7 @@
 
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/threading/non_thread_safe.h"
 #include "ui/gfx/image/image_skia_operations.h"
 #include "ui/gfx/image/image_skia_source.h"
 #include "ui/gfx/rect.h"
@@ -48,11 +49,15 @@ class Matcher {
 // A helper class such that ImageSkia can be cheaply copied. ImageSkia holds a
 // refptr instance of ImageSkiaStorage, which in turn holds all of ImageSkia's
 // information.
-class ImageSkiaStorage : public base::RefCounted<ImageSkiaStorage> {
+class ImageSkiaStorage : public base::RefCounted<ImageSkiaStorage>,
+                         public base::NonThreadSafe {
  public:
   ImageSkiaStorage(ImageSkiaSource* source, const gfx::Size& size)
       : source_(source),
         size_(size) {
+    // We only care if the storage is modified by the same thread.
+    // Don't blow up even if someone else created/deleted the ImageSkia.
+    base::NonThreadSafe::DetachFromThread();
   }
 
   bool has_source() const { return source_.get() != NULL; }
@@ -61,6 +66,17 @@ class ImageSkiaStorage : public base::RefCounted<ImageSkiaStorage> {
 
   const gfx::Size& size() const { return size_; }
 
+  // A public method to call base::NonThreadSafeImpl::DetachFromThread
+  // which is protected.  See base/threading/non_thread_safe_impl.h
+  // for more details.
+  void DetachFromThread() {
+    base::NonThreadSafe::DetachFromThread();
+  }
+
+  void DeleteSource() {
+    source_.reset();
+  }
+
   // Returns the iterator of the image rep whose density best matches
   // |scale_factor|. If the image for the |scale_factor| doesn't exist
   // in the storage and |storage| is set, it fetches new image by calling
@@ -96,6 +112,10 @@ class ImageSkiaStorage : public base::RefCounted<ImageSkiaStorage> {
     }
 
     if (fetch_new_image && source_.get()) {
+      DCHECK(CalledOnValidThread()) <<
+          "More than one thread is tring to access ImageSkia which has "
+          "ImageSkiaSource. This is thread unsafe operation and not allowed";
+
       ImageSkiaRep image = source_->GetImageForScale(scale_factor);
 
       // If the source returned the new image, store it.
@@ -120,7 +140,8 @@ class ImageSkiaStorage : public base::RefCounted<ImageSkiaStorage> {
   }
 
  private:
-  ~ImageSkiaStorage() {
+  virtual ~ImageSkiaStorage() {
+    DetachFromThread();
   }
 
   // Vector of bitmaps and their associated scale factor.
@@ -223,14 +244,7 @@ std::vector<ImageSkiaRep> ImageSkia::GetRepresentations() const {
   if (!storage_->has_source())
     return image_reps();
 
-  // Attempt to generate image reps for as many scale factors supported by
-  // this platform as possible.
-  // Do not build return array here because the mapping from scale factor to
-  // image rep is one to many in some cases.
-  std::vector<ui::ScaleFactor> supported_scale_factors =
-      ui::GetSupportedScaleFactors();
-  for (size_t i = 0; i < supported_scale_factors.size(); ++i)
-    storage_->FindRepresentation(supported_scale_factors[i], true);
+  EnsureRepsForSupportedScaleFactors();
 
   return image_reps();
 }
@@ -266,6 +280,20 @@ std::vector<ImageSkiaRep> ImageSkia::image_reps() const {
   return image_reps;
 }
 
+void ImageSkia::DeleteSource() {
+  if (storage_)
+    storage_->DeleteSource();
+}
+
+void ImageSkia::EnsureRepsForSupportedScaleFactors() const {
+  if (storage_ && storage_->has_source()) {
+    std::vector<ui::ScaleFactor> supported_scale_factors =
+        ui::GetSupportedScaleFactors();
+    for (size_t i = 0; i < supported_scale_factors.size(); ++i)
+      storage_->FindRepresentation(supported_scale_factors[i], true);
+  }
+}
+
 void ImageSkia::Init(const ImageSkiaRep& image_rep) {
   // TODO(pkotwicz): The image should be null whenever image rep is null.
   if (image_rep.sk_bitmap().empty()) {