cc: Implement tiling iterator based on pyramid sequence.

cc/base/index_rect.cc

Index: cc/base/index_rect.cc
diff --git a/cc/base/index_rect.cc b/cc/base/index_rect.cc
index 0c64c42a1b03efab8c0efc881e98216a4e578351..a2613ed49ef6323d4bbc2fcf31162e5751a84d90 100644
--- a/cc/base/index_rect.cc
+++ b/cc/base/index_rect.cc
@@ -7,6 +7,7 @@
 #include <algorithm>
 
 #include "base/strings/stringprintf.h"
+#include "ui/gfx/geometry/safe_integer_conversions.h"
 
 namespace cc {
 
@@ -22,6 +23,13 @@ bool IndexRect::Contains(int index_x, int index_y) const {
          index_y <= bottom_;
 }
 
+void IndexRect::Inset(int left, int right, int top, int bottom) {
+  left_ = gfx::SafeAdd(left_, left);
+  right_ = gfx::SafeSubtract(right_, right);
+  top_ = gfx::SafeAdd(top_, top);
+  bottom_ = gfx::SafeSubtract(bottom_, bottom);
+}
+
 std::string IndexRect::ToString() const {
   return base::StringPrintf("%d,%d,%d,%d", left(), right(), top(), bottom());
 }