Make InlineBoxPosition constructor not to accept null-InlineBox

third_party/WebKit/Source/core/editing/VisibleUnits.h

Index: third_party/WebKit/Source/core/editing/VisibleUnits.h
diff --git a/third_party/WebKit/Source/core/editing/VisibleUnits.h b/third_party/WebKit/Source/core/editing/VisibleUnits.h
index 16e3a9e499db51575e161d09c89b7ffb27efdc65..77618f7264d228375dbc362c4fca12df683bb2de 100644
--- a/third_party/WebKit/Source/core/editing/VisibleUnits.h
+++ b/third_party/WebKit/Source/core/editing/VisibleUnits.h
@@ -52,7 +52,10 @@ struct InlineBoxPosition {
   InlineBoxPosition() : inline_box(nullptr), offset_in_box(0) {}
 
   InlineBoxPosition(InlineBox* inline_box, int offset_in_box)
-      : inline_box(inline_box), offset_in_box(offset_in_box) {}
+      : inline_box(inline_box), offset_in_box(offset_in_box) {
+    DCHECK(inline_box);
+    DCHECK_GE(offset_in_box, 0);
+  }
 
   bool operator==(const InlineBoxPosition& other) const {
     return inline_box == other.inline_box &&