Bug 1399626 - Part 6: Stop asserting that RangeBoundary objects are valid as they are created, r=masayuki

This is necessary, as we now use RangeBoundary objects as intermediate types to
pass (parent,offset) pairs into constructors for nsRange. We are allowed to try
to construct invalid nsRange objects, but unfortunately doing so would fire an
assertion if we don't allow constructing invalid RangeBoundary objects.

It's possible to check if the RangeBoundary object is valid by calling
`IsSetAndValid`, which should be done for error checking when you don't trust
the source of the RangeBoundary object anyway.

MozReview-Commit-ID: 3Pf80ndRZLW

dom/base/RangeBoundary.h

@@ -56,6 +56,8 @@ public:
     if (!mRef) {
       mOffset = mozilla::Some(0);
     } else {
+      NS_WARNING_ASSERTION(mRef->GetParentNode() == mParent,
+                           "Initializing RangeBoundary with invalid value");
       mOffset.reset();
     }
   }
@@ -71,13 +73,14 @@ public:
         mRef = aContainer->GetLastChild();
       } else if (aOffset != 0) {
         mRef = mParent->GetChildAt(aOffset - 1);
-        MOZ_ASSERT(mRef);
       }
 
-      MOZ_ASSERT_IF(!mRef, aOffset == 0);
+      NS_WARNING_ASSERTION(mRef || aOffset == 0,
+                           "Constructing RangeBoundary with invalid value");
     }
 
-    MOZ_ASSERT_IF(mRef, mRef->GetParentNode() == mParent);
+    NS_WARNING_ASSERTION(!mRef || mRef->GetParentNode() == mParent,
+                         "Constructing RangeBoundary with invalid value");
   }
 
   RangeBoundaryBase()
@@ -114,7 +117,7 @@ public:
       return nullptr;
     }
     if (!mRef) {
-      MOZ_ASSERT(Offset() == 0);
+      MOZ_ASSERT(Offset() == 0, "invalid RangeBoundary");
       return mParent->GetFirstChild();
     }
     MOZ_ASSERT(mParent->GetChildAt(Offset()) == mRef->GetNextSibling());
@@ -146,7 +149,8 @@ public:
     MOZ_ASSERT(mParent->IsContainerNode(), "Range is positioned on a text node!");
 
     if (!mRef) {
-      MOZ_ASSERT(mOffset.isSome() && mOffset.value() == 0);
+      MOZ_ASSERT(mOffset.isSome() && mOffset.value() == 0,
+                 "Invalidating offset of invalid RangeBoundary?");
       return;
     }
     mOffset.reset();
@@ -167,13 +171,16 @@ public:
         MOZ_ASSERT(mRef);
       }
 
-      MOZ_ASSERT_IF(!mRef, aOffset == 0);
+      NS_WARNING_ASSERTION(mRef || aOffset == 0,
+                           "Setting RangeBoundary to invalid value");
     } else {
       mRef = nullptr;
     }
 
     mOffset = mozilla::Some(aOffset);
-    MOZ_ASSERT_IF(mRef, mRef->GetParentNode() == mParent);
+
+    NS_WARNING_ASSERTION(!mRef || mRef->GetParentNode() == mParent,
+                         "Setting RangeBoundary to invalid value");
   }
 
   void