A host of micro-optimizations and a refactor of TimeForBoundsToIntersect

cc/tile_priority.h

Index: cc/tile_priority.h
diff --git a/cc/tile_priority.h b/cc/tile_priority.h
index fb900608eb175b42ce0ba5d587378ab923b93a31..e5e0bb8a41c6f4b43fc711438b1d2d02df200c00 100644
--- a/cc/tile_priority.h
+++ b/cc/tile_priority.h
@@ -61,17 +61,30 @@ struct CC_EXPORT TilePriority {
                     time_to_ideal_resolution_in_seconds);
   }
 
-  static const double kMaxTimeToVisibleInSeconds;
-
-  static int manhattanDistance(const gfx::RectF& a, const gfx::RectF& b);
+  static const float kMaxTimeToVisibleInSeconds;
+
+  static inline float manhattanDistance(const gfx::RectF& a, const gfx::RectF& b) {
+    // Compute the union explicitly.
+    gfx::RectF c = gfx::RectF(
+        std::min(a.x(), b.x()),
+        std::min(a.y(), b.y()),
+        std::max(a.right(), b.right() - std::min(a.x(), b.x())),
+        std::max(a.bottom(), b.bottom() - std::min(a.y(), b.y())));
+
+    // Rects touching the edge of the screen should not be considered visible.
+    // So we add 1 pixel here to avoid that situation.
+    float x = std::max(0.0f, c.width() - a.width() - b.width() + 1.0f);
+    float y = std::max(0.0f, c.height() - a.height() - b.height() + 1.0f);
+    return (x + y);
+  }
 
   // Calculate the time for the |current_bounds| to intersect with the
   // |target_bounds| given its previous location and time delta.
   // This function should work for both scaling and scrolling case.
-  static double TimeForBoundsToIntersect(gfx::RectF previous_bounds,
-                                         gfx::RectF current_bounds,
-                                         double time_delta,
-                                         gfx::RectF target_bounds);
+  static float TimeForBoundsToIntersect(const gfx::RectF& previous_bounds,
+                                        const gfx::RectF& current_bounds,
+                                        float time_delta,
+                                        const gfx::RectF& target_bounds);
 
   TileResolution resolution;
   float time_to_visible_in_seconds;