Merge pull request #769 from pkasting/metadata

Fix compile failures building protobuf DLLs on MSVC in Chromium's cod…

src/google/protobuf/metadata.h

@@ -56,7 +56,7 @@ namespace internal {
 // The tagged pointer uses the LSB to disambiguate cases, and uses bit 0 == 0 to
 // indicate an arena pointer and bit 0 == 1 to indicate a UFS+Arena-container
 // pointer.
-class LIBPROTOBUF_EXPORT InternalMetadataWithArena {
+class InternalMetadataWithArena {
  public:
   InternalMetadataWithArena() : ptr_(NULL) {}
   explicit InternalMetadataWithArena(Arena* arena)