Give UnownedPtr<> a move ctor and move assign operator.

Otherwise, the examples added to the unit test will trip an
incorrect asssertion.

Change-Id: I1dc85cfdf0937036c4493e43ee9dfac03ec38767
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/63156
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>

core/fxcrt/unowned_ptr.h

diff --git a/core/fxcrt/unowned_ptr.h b/core/fxcrt/unowned_ptr.h
index 7bbd937..5a8ee3d 100644
--- a/core/fxcrt/unowned_ptr.h
+++ b/core/fxcrt/unowned_ptr.h
@@ -49,6 +49,7 @@
  public:
   constexpr UnownedPtr() noexcept = default;
   constexpr UnownedPtr(const UnownedPtr& that) noexcept = default;
+  constexpr UnownedPtr(UnownedPtr&& that) noexcept : m_pObj(that.Release()) {}
 
   template <typename U>
   explicit constexpr UnownedPtr(U* pObj) noexcept : m_pObj(pObj) {}
@@ -75,6 +76,12 @@
     return *this;
   }
 
+  UnownedPtr& operator=(UnownedPtr&& that) noexcept {
+    if (*this != that)
+      Reset(that.Release());
+    return *this;
+  }
+
   bool operator==(const UnownedPtr& that) const { return Get() == that.Get(); }
   bool operator!=(const UnownedPtr& that) const { return !(*this == that); }
   bool operator<(const UnownedPtr& that) const {

core/fxcrt/unowned_ptr_unittest.cpp

diff --git a/core/fxcrt/unowned_ptr_unittest.cpp b/core/fxcrt/unowned_ptr_unittest.cpp
index c125873..f1979ef 100644
--- a/core/fxcrt/unowned_ptr_unittest.cpp
+++ b/core/fxcrt/unowned_ptr_unittest.cpp
@@ -114,6 +114,25 @@
   }
 }
 
+TEST(UnownedPtr, MoveCtorOk) {
+  UnownedPtr<Clink> outer;
+  {
+    auto owned = pdfium::MakeUnique<Clink>();
+    outer = owned.get();
+    UnownedPtr<Clink> inner(std::move(outer));
+  }
+}
+
+TEST(UnownedPtr, MoveAssignOk) {
+  UnownedPtr<Clink> outer;
+  {
+    auto owned = pdfium::MakeUnique<Clink>();
+    outer = owned.get();
+    UnownedPtr<Clink> inner;
+    inner = std::move(outer);
+  }
+}
+
 TEST(UnownedPtr, ReleaseNotOk) {
 #if defined(ADDRESS_SANITIZER)
   EXPECT_DEATH(ReleaseDangling(), "");