gfx::Image: Added thread checker.

chrome/browser/themes/browser_theme_pack.cc

Index: chrome/browser/themes/browser_theme_pack.cc
diff --git a/chrome/browser/themes/browser_theme_pack.cc b/chrome/browser/themes/browser_theme_pack.cc
index 8b72d3c7d82487ad3c957f0f456df4682ffe917a..7227d64ae1ec4539ac674ea551bdc79180bdfe01 100644
--- a/chrome/browser/themes/browser_theme_pack.cc
+++ b/chrome/browser/themes/browser_theme_pack.cc
@@ -537,6 +537,8 @@ class TabBackgroundImageSource: public gfx::CanvasImageSource {
 }  // namespace
 
 BrowserThemePack::~BrowserThemePack() {
+  DCHECK_CURRENTLY_ON(BrowserThread::FILE);
+
   if (!data_pack_.get()) {
     delete header_;
     delete [] tints_;
@@ -544,6 +546,20 @@ BrowserThemePack::~BrowserThemePack() {
     delete [] display_properties_;
     delete [] source_images_;
   }
+
+  // |images_| will trigger the thread-checker as the images were built on the
+  // UI thread and we are on the FILE thread. As a special case, it is safe to
+  // delete them on the FILE thread because there are no remaining references to
+  // this BrowserThemePack from the UI thread. Explicitly detach all the images
+  // from the UI thread to suppress the error.
+  for (auto image : images_)
+    image.second.DetachFromThread();
+
+  // For the same reason, detach all of the |images_on_file_thread_| from
+  // whatever thread they are attached to. (Note that |images_on_file_thread_|
+  // is usually accessed on the FILE thread, but not always.)
+  for (auto image : images_on_file_thread_)
+    image.second.DetachFromThread();
 }
 
 // static
@@ -594,6 +610,9 @@ void BrowserThemePack::BuildFromExtension(
     ThemeImageSource* source = new ThemeImageSource(source_image_skia);
     // image_skia takes ownership of source.
     gfx::ImageSkia image_skia(source, source_image_skia.size());
+    // From now on, it->second will only be stored in |images_on_file_thread_|,
+    // so detach it from the UI thread.
+    it->second.DetachFromThread();
     it->second = gfx::Image(image_skia);
   }