Add a move constructor and move assignment operator to Length

Source/platform/Length.h

Index: Source/platform/Length.h
diff --git a/Source/platform/Length.h b/Source/platform/Length.h
index 9104f3b4e2d89567b61c989713778b1553eaac5f..40183bc8e6d57f4d79bb598814bf4b0dc6ae10d5 100644
--- a/Source/platform/Length.h
+++ b/Source/platform/Length.h
@@ -120,6 +120,27 @@ public:
         return *this;
     }
 
+#if COMPILER_SUPPORTS(CXX_RVALUE_REFERENCES)
+    Length(Length&& length)
+    {
+        memcpy(this, &length, sizeof(Length));
+        length.m_type = Auto;

[tkent, 2014/05/27 00:13:29]

Why do we need do length.m_type=Auto though |length| is rvalue?

[Inactive, 2014/05/27 00:33:29]

We basically want to make sure that |length|'s destructor won't call
decrementCalculatedRef() (as isCalculated() check will fail) since we don't call
length.incrementCalculatedRef() here.

+    }
+
+    Length& operator=(Length&& length)
+    {
+        if (this == &length)
+            return *this;
+
+        if (isCalculated())
+            decrementCalculatedRef();
+
+        memcpy(this, &length, sizeof(Length));
+        length.m_type = Auto;

[tkent, 2014/05/27 00:13:29]

Ditto.

I understand length.incrementCalculatedRef() is unnecessary in this case.

+        return *this;
+    }
+#endif
+
     ~Length()
     {
         if (isCalculated())