implement the logic to set tile priorities based on current matrix

cc/picture_layer_tiling_unittest.cc

Index: cc/picture_layer_tiling_unittest.cc
diff --git a/cc/picture_layer_tiling_unittest.cc b/cc/picture_layer_tiling_unittest.cc
index 03bd9aadb19d29f4e3b66b937cebed9e34fbda57..2e45af960348eba6d1c662b34999c534ec89bf42 100644
--- a/cc/picture_layer_tiling_unittest.cc
+++ b/cc/picture_layer_tiling_unittest.cc
@@ -64,6 +64,23 @@ class PictureLayerTilingIteratorTest : public testing::Test {
   DISALLOW_COPY_AND_ASSIGN(PictureLayerTilingIteratorTest);
 };
 
+class PictureLayerTilingTest : public testing::Test {
+ public:
+  PictureLayerTilingTest() {
+    tiling_ = PictureLayerTiling::Create(0, gfx::Size(0, 0));
+  }
+
+  void VerifyTimeForBoundsToIntersect(gfx::Rect previous,
+                                      gfx::Rect current,
+                                      gfx::Rect target,
+                                      double time) {
+    EXPECT_EQ(tiling_->TimeForBoundsToIntersect(previous, current, 1, target),
+              time);
+  }
+ protected:
+  scoped_ptr<PictureLayerTiling> tiling_;
+};
+
 TEST_F(PictureLayerTilingIteratorTest, IteratorCoversLayerBoundsNoScale) {
   Initialize(gfx::Size(100, 100), 1, gfx::Size(1099, 801));
   VerifyTilesExactlyCoverRect(1, gfx::Rect());
@@ -118,4 +135,42 @@ TEST_F(PictureLayerTilingIteratorTest, IteratorCoversLayerBoundsBothScale) {
   VerifyTilesExactlyCoverRect(scale, gfx::Rect(2014, 1579, 867, 1033));
 }
 
+TEST_F(PictureLayerTilingTest, TimeForBoundsToIntersectWithScroll) {
+  gfx::Rect target(0, 0, 800, 600);
+  gfx::Rect current(100, 100, 100, 100);
+  VerifyTimeForBoundsToIntersect(
+      gfx::Rect(-200, 0, 100, 100), current, target, 0);
+  VerifyTimeForBoundsToIntersect(
+      gfx::Rect(-100, 0, 100, 100), current, target, 0);
+  VerifyTimeForBoundsToIntersect(
+      gfx::Rect(400, 400, 100, 100), current, target, 0);
+
+  current = gfx::Rect(-300, -300, 100, 100);
+  VerifyTimeForBoundsToIntersect(
+      gfx::Rect(0, 0, 100, 100), current, target, 1000);
+  VerifyTimeForBoundsToIntersect(
+      gfx::Rect(-200, -200, 100, 100), current, target, 1000);
+  VerifyTimeForBoundsToIntersect(
+      gfx::Rect(-400, -400, 100, 100), current, target, 2);
+}
+
+TEST_F(PictureLayerTilingTest, TimeForBoundsToIntersectWithScale) {
+  gfx::Rect target(0, 0, 800, 600);
+  gfx::Rect current(100, 100, 100, 100);
+  VerifyTimeForBoundsToIntersect(
+      gfx::Rect(-200, 0, 200, 200), current, target, 0);
+  VerifyTimeForBoundsToIntersect(
+      gfx::Rect(-100, 0, 50, 50), current, target, 0);
+  VerifyTimeForBoundsToIntersect(
+      gfx::Rect(400, 400, 400, 400), current, target, 0);
+
+  current = gfx::Rect(-300, -300, 100, 100);
+  VerifyTimeForBoundsToIntersect(
+      gfx::Rect(-400, -400, 300, 300), current, target, 1000);
+  VerifyTimeForBoundsToIntersect(
+      gfx::Rect(-275, -275, 50, 50), current, target, 8);
+  VerifyTimeForBoundsToIntersect(
+      gfx::Rect(-450, -450, 50, 50), current, target, 1);
+}
+
 }  // namespace cc