Switch gfx::Range to use uint32_t instead of size_t.

ui/gfx/selection_model.h

Index: ui/gfx/selection_model.h
diff --git a/ui/gfx/selection_model.h b/ui/gfx/selection_model.h
index 87a7a2d0b4e2449c08b57df968c75860181af94e..73bf113da5cdd782dc175c7738a2f66935f9c2c6 100644
--- a/ui/gfx/selection_model.h
+++ b/ui/gfx/selection_model.h
@@ -77,7 +77,7 @@ class GFX_EXPORT SelectionModel {
 
   // WARNING: Generally the selection start should not be changed without
   // considering the effect on the caret affinity.
-  void set_selection_start(size_t pos) { selection_.set_start(pos); }
+  void set_selection_start(uint32_t pos) { selection_.set_start(pos); }
 
   bool operator==(const SelectionModel& sel) const;
   bool operator!=(const SelectionModel& sel) const { return !(*this == sel); }