Refactored-out the code of thumbnaling algorithm from thumbnail_tab_helper.

chrome/browser/thumbnails/thumbnail_service.h

Index: chrome/browser/thumbnails/thumbnail_service.h
diff --git a/chrome/browser/thumbnails/thumbnail_service.h b/chrome/browser/thumbnails/thumbnail_service.h
index 53da3e637e590bb942354d8071b5a711a04588ca..aa27310dfccc300922c4c5f0b0324ec44f64063a 100644
--- a/chrome/browser/thumbnails/thumbnail_service.h
+++ b/chrome/browser/thumbnails/thumbnail_service.h
@@ -16,6 +16,9 @@ class RefCountedMemory;
 
 namespace thumbnails {
 
+class ThumbnailingAlgorithm;
+class ThumbnailingContext;
+
 // An interface abstracting access to thumbnails. Intended as a temporary
 // bridge facilitating switch from TopSites as the thumbnail source to a more
 // robust way of handling these artefacts.
@@ -24,9 +27,13 @@ class ThumbnailService : public RefcountedProfileKeyedService {
   // Sets the given thumbnail for the given URL. Returns true if the thumbnail
   // was updated. False means either the URL wasn't known to us, or we felt
   // that our current thumbnail was superior to the given one.
-  virtual bool SetPageThumbnail(const GURL& url,
-                                const gfx::Image& thumbnail,
-                                const ThumbnailScore& score) = 0;
+  virtual bool SetPageThumbnail(const ThumbnailingContext& context,
+                                const gfx::Image& thumbnail) = 0;
+
+  // Create and return a new instance of the algorithm. These objects are
+  // lightweight and are expected to self-destruct. They encapsulate the process
+  // of creating a thumbnail from tab contents.
+  virtual ThumbnailingAlgorithm* CreateThumbnailingAlgorithm() const = 0;
 
   // Gets a thumbnail for a given page. Returns true iff we have the thumbnail.
   // This may be invoked on any thread.