Prevent segfaults due to bad pointer conversion with inheritance.

If we pass a View* through a void*, we need to cast to View* on the
other side before any casting to a View subclass, or the pointer will
not be fixed up correctly.

In this case, we can just pass as a View* directly, avoiding the void*,
and the cast-to-derived Just Works.

Found this while trying to add metadata to OmniboxViewViews, which
inherits from views::Textfield but does not have that as the first base
class.

Bug: none
Change-Id: I5abc3efc3abbbe470ab23b3579984767f9e51b1b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2625752
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Wei Li <weili@chromium.org>
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Wei Li <weili@chromium.org>
Cr-Commit-Position: refs/heads/master@{#842873}

ui/views/metadata/metadata_types.cc

@@ -137,7 +137,7 @@ void ClassMetaData::SetTypeName(const std::string& type_name) {
   type_name_ = type_name;
 }
 
-void MemberMetaDataBase::SetValueAsString(void* obj,
+void MemberMetaDataBase::SetValueAsString(View* obj,
                                           const base::string16& new_value) {
   NOTREACHED();
 }

ui/views/metadata/metadata_types.h

@@ -14,6 +14,9 @@
 #include "ui/views/views_export.h"
 
 namespace views {
+
+class View;
+
 namespace metadata {
 
 enum class PropertyFlags : uint32_t {
@@ -151,12 +154,12 @@ class VIEWS_EXPORT MemberMetaDataBase {
   // Access the value of this member and return it as a string.
   // |obj| is the instance on which to obtain the value of the property this
   // metadata represents.
-  virtual base::string16 GetValueAsString(void* obj) const = 0;
+  virtual base::string16 GetValueAsString(View* obj) const = 0;
 
   // Set the value of this member through a string on a specified object.
   // |obj| is the instance on which to set the value of the property this
   // metadata represents.
-  virtual void SetValueAsString(void* obj, const base::string16& new_value);
+  virtual void SetValueAsString(View* obj, const base::string16& new_value);
 
   // Return various information flags about the property.
   virtual PropertyFlags GetPropertyFlags() const = 0;

ui/views/metadata/property_metadata.h

@@ -14,6 +14,7 @@
 #include "ui/views/metadata/metadata_cache.h"
 #include "ui/views/metadata/metadata_types.h"
 #include "ui/views/metadata/type_conversion.h"
+#include "ui/views/view.h"
 #include "ui/views/views_export.h"
 
 namespace views {
@@ -32,7 +33,7 @@ class ClassPropertyReadOnlyMetaData : public MemberMetaDataBase {
   using MemberMetaDataBase::MemberMetaDataBase;
   ~ClassPropertyReadOnlyMetaData() override = default;
 
-  base::string16 GetValueAsString(void* obj) const override {
+  base::string16 GetValueAsString(View* obj) const override {
     if (!kIsSerializable)
       return base::string16();
     return TypeConverter<TValue>::ToString((static_cast<TClass*>(obj)->*Get)());
@@ -69,7 +70,7 @@ class ClassPropertyMetaData
       ClassPropertyReadOnlyMetaData;
   ~ClassPropertyMetaData() override = default;
 
-  void SetValueAsString(void* obj, const base::string16& new_value) override {
+  void SetValueAsString(View* obj, const base::string16& new_value) override {
     if (!kIsSerializable)
       return;
     if (base::Optional<TValue> result =