Add heuristics to skip thumbnail generation when it's unnecessary.

chrome/browser/tab_contents/thumbnail_generator_unittest.cc

Index: chrome/browser/tab_contents/thumbnail_generator_unittest.cc
diff --git a/chrome/browser/tab_contents/thumbnail_generator_unittest.cc b/chrome/browser/tab_contents/thumbnail_generator_unittest.cc
index 7c7f60185df41131651fbaf014d9dc73315a4fd5..8d0fbe48c084db76b18a2f9151281f20ca87c6d4 100644
--- a/chrome/browser/tab_contents/thumbnail_generator_unittest.cc
+++ b/chrome/browser/tab_contents/thumbnail_generator_unittest.cc
@@ -4,6 +4,8 @@
 
 #include "app/surface/transport_dib.h"
 #include "base/basictypes.h"
+#include "base/stringprintf.h"
+#include "chrome/browser/history/top_sites.h"
 #include "chrome/browser/renderer_host/backing_store_manager.h"
 #include "chrome/browser/renderer_host/mock_render_process_host.h"
 #include "chrome/browser/renderer_host/test/test_render_view_host.h"
@@ -278,3 +280,100 @@ TEST(ThumbnailGeneratorSimpleTest, GetClippedBitmap_NonSquareOutput) {
   // The input was taller than wide.
   EXPECT_EQ(ThumbnailGenerator::kTallerThanWide, clip_result);
 }
+
+// A mock version of TopSites, used for testing ShouldUpdateThumbnail().
+class MockTopSites : public history::TopSites {
+ public:
+  MockTopSites(Profile* profile)
+      : history::TopSites(profile),
+        capacity_(1) {
+  }
+
+  // history::TopSites overrides.
+  virtual bool IsFull() {
+    return known_url_map_.size() >= capacity_;
+  }
+  virtual bool IsKnownURL(const GURL& url) {
+    return known_url_map_.find(url.spec()) != known_url_map_.end();
+  }
+  virtual bool GetPageThumbnailScore(const GURL& url, ThumbnailScore* score) {
+    std::map<std::string, ThumbnailScore>::const_iterator iter =
+        known_url_map_.find(url.spec());
+    if (iter == known_url_map_.end()) {
+      return false;
+    } else {
+      *score = iter->second;
+      return true;
+    }
+  }
+
+  // Adds a known URL with the associated thumbnail score.
+  void AddKnownURL(const GURL& url, const ThumbnailScore& score) {
+    known_url_map_[url.spec()] = score;
+  }
+
+ private:
+  virtual ~MockTopSites() {}
+  size_t capacity_;
+  std::map<std::string, ThumbnailScore> known_url_map_;
+};
+
+TEST(ThumbnailGeneratorSimpleTest, ShouldUpdateThumbnail) {
+  const GURL kGoodURL("http://www.google.com/");
+  const GURL kBadURL("chrome://newtab");
+
+  // Set up the profile.
+  TestingProfile profile;
+
+  // Set up the top sites service.
+  ScopedTempDir temp_dir;
+  ASSERT_TRUE(temp_dir.CreateUniqueTempDir());
+  scoped_refptr<MockTopSites> top_sites(new MockTopSites(&profile));
+
+  // Should be false because it's a bad URL.
+  EXPECT_FALSE(ThumbnailGenerator::ShouldUpdateThumbnail(
+      &profile, top_sites.get(), kBadURL));
+
+  // Should be true, as it's a good URL.
+  EXPECT_TRUE(ThumbnailGenerator::ShouldUpdateThumbnail(
+      &profile, top_sites.get(), kGoodURL));
+
+  // Should be false, if it's in the off-the-record mode.
+  profile.set_off_the_record(true);
+  EXPECT_FALSE(ThumbnailGenerator::ShouldUpdateThumbnail(
+      &profile, top_sites.get(), kGoodURL));
+
+  // Should be true again, once turning off the off-the-record mode.
+  profile.set_off_the_record(false);
+  EXPECT_TRUE(ThumbnailGenerator::ShouldUpdateThumbnail(
+      &profile, top_sites.get(), kGoodURL));
+
+  // Add a known URL. This makes the top sites data full.
+  ThumbnailScore bad_score;
+  bad_score.time_at_snapshot = base::Time::UnixEpoch();  // Ancient time stamp.
+  top_sites->AddKnownURL(kGoodURL, bad_score);
+  ASSERT_TRUE(top_sites->IsFull());
+
+  // Should be false, as the top sites data is full, and the new URL is
+  // not known.
+  const GURL kAnotherGoodURL("http://www.youtube.com/");
+  EXPECT_FALSE(ThumbnailGenerator::ShouldUpdateThumbnail(
+      &profile, top_sites.get(), kAnotherGoodURL));
+
+  // Should be true, as the existing thumbnail is bad (i.e need a better one).
+  EXPECT_TRUE(ThumbnailGenerator::ShouldUpdateThumbnail(
+      &profile, top_sites.get(), kGoodURL));
+
+  // Replace the thumbnail score with a really good one.
+  ThumbnailScore good_score;
+  good_score.time_at_snapshot = base::Time::Now();  // Very new.
+  good_score.at_top = true;
+  good_score.good_clipping = true;
+  good_score.boring_score = 0.0;
+  top_sites->AddKnownURL(kGoodURL, good_score);
+
+  // Should be false, as the existing thumbnail is good enough (i.e. don't
+  // need to replace the existing thumbnail which is new and good).
+  EXPECT_FALSE(ThumbnailGenerator::ShouldUpdateThumbnail(
+      &profile, top_sites.get(), kGoodURL));
+}