Add missing operator<() to CFX_RetainPtr.

Use std::less<>() rather than a direct ptr1 < ptr2 comparison to
be strictly correct in face of unspecified behaviour when ptr1 and
ptr2 don't point within the same "object" (e.g. segment of memory
on a brain-dead segmented architecture).

This will allow their use as keys in maps.

Review-Url: https://codereview.chromium.org/2616683002

2 files changed, 14 insertions, 1 deletions

diff --git a/core/fxcrt/cfx_retain_ptr.h b/core/fxcrt/cfx_retain_ptr.h
index 1b137d4974..f70faf1464 100644
--- a/core/fxcrt/cfx_retain_ptr.h
+++ b/core/fxcrt/cfx_retain_ptr.h
@@ -5,11 +5,13 @@
 #ifndef CORE_FXCRT_CFX_RETAIN_PTR_H_
 #define CORE_FXCRT_CFX_RETAIN_PTR_H_
 
+#include <functional>
 #include <memory>
 #include <utility>
 
 #include "core/fxcrt/fx_memory.h"
 
+// Analogous to base's scoped_refptr.
 template <class T>
 class CFX_RetainPtr {
  public:
@@ -50,9 +52,12 @@ class CFX_RetainPtr {
   bool operator==(const CFX_RetainPtr& that) const {
     return Get() == that.Get();
   }
-
   bool operator!=(const CFX_RetainPtr& that) const { return !(*this == that); }
 
+  bool operator<(const CFX_RetainPtr& that) const {
+    return std::less<T*>()(Get(), that.Get());
+  }
+
   explicit operator bool() const { return !!m_pObj; }
   T& operator*() const { return *m_pObj.get(); }
   T* operator->() const { return m_pObj.get(); }
diff --git a/core/fxcrt/cfx_retain_ptr_unittest.cpp b/core/fxcrt/cfx_retain_ptr_unittest.cpp
index f9a4ecb74f..3168b5a4c7 100644
--- a/core/fxcrt/cfx_retain_ptr_unittest.cpp
+++ b/core/fxcrt/cfx_retain_ptr_unittest.cpp
@@ -225,6 +225,14 @@ TEST(fxcrt, RetainPtrNotEquals) {
   EXPECT_TRUE(obj1_ptr1 != obj2_ptr1);
 }
 
+TEST(fxcrt, RetainPtrLessThan) {
+  PseudoRetainable objs[2];
+  CFX_RetainPtr<PseudoRetainable> obj1_ptr(&objs[0]);
+  CFX_RetainPtr<PseudoRetainable> obj2_ptr(&objs[1]);
+  EXPECT_TRUE(obj1_ptr < obj2_ptr);
+  EXPECT_FALSE(obj2_ptr < obj1_ptr);
+}
+
 TEST(fxcrt, RetainPtrBool) {
   PseudoRetainable obj1;
   CFX_RetainPtr<PseudoRetainable> null_ptr;