Fix compile failures building protobuf DLLs on MSVC in Chromium's codebase.

When trying to compile the protobuf code as a DLL, and then compile other DLLs
with generated .pb.cc/h files that reference
InternalMetadataWithArena::InternalMetadataWithArena(Arena*), MSVC gives an
"unresolved external symbol" error.  This seems to be due to the function being
simultaneously exported and inline.  Moving it out-of-line fixes things.

There are other functions exported and inline as well but de-inlining them
doesn't seem to be necessary to get the build working, and I'd rather de-inline
as few functions as possible.

BUILD

@@ -30,6 +30,7 @@ cc_library(
         "src/google/protobuf/io/zero_copy_stream.cc",
         "src/google/protobuf/io/zero_copy_stream_impl_lite.cc",
         "src/google/protobuf/message_lite.cc",
+        "src/google/protobuf/metadata.cc",
         "src/google/protobuf/repeated_field.cc",
         "src/google/protobuf/stubs/atomicops_internals_x86_gcc.cc",
         "src/google/protobuf/stubs/atomicops_internals_x86_msvc.cc",

cmake/libprotobuf-lite.cmake

@@ -7,6 +7,7 @@ set(libprotobuf_lite_files
   ${protobuf_source_dir}/src/google/protobuf/io/zero_copy_stream.cc
   ${protobuf_source_dir}/src/google/protobuf/io/zero_copy_stream_impl_lite.cc
   ${protobuf_source_dir}/src/google/protobuf/message_lite.cc
+  ${protobuf_source_dir}/src/google/protobuf/metadata.cc
   ${protobuf_source_dir}/src/google/protobuf/repeated_field.cc
   ${protobuf_source_dir}/src/google/protobuf/stubs/atomicops_internals_x86_gcc.cc
   ${protobuf_source_dir}/src/google/protobuf/stubs/atomicops_internals_x86_msvc.cc

src/Makefile.am

@@ -196,6 +196,7 @@ libprotobuf_lite_la_SOURCES =                                  \
   google/protobuf/extension_set.cc                             \
   google/protobuf/generated_message_util.cc                    \
   google/protobuf/message_lite.cc                              \
+  google/protobuf/metadata.cc                                  \
   google/protobuf/repeated_field.cc                            \
   google/protobuf/wire_format_lite.cc                          \
   google/protobuf/io/coded_stream.cc                           \

src/google/protobuf/metadata.cc

@@ -0,0 +1,42 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2015 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include <google/protobuf/metadata.h>
+
+namespace google {
+namespace protobuf {
+namespace internal {
+
+InternalMetadataWithArena::InternalMetadataWithArena(Arena* arena)
+    : ptr_(arena) {}
+
+}  // namespace internal
+}  // namespace protobuf
+}  // namespace google

src/google/protobuf/metadata.h

@@ -59,8 +59,7 @@ namespace internal {
 class LIBPROTOBUF_EXPORT InternalMetadataWithArena {
  public:
   InternalMetadataWithArena() : ptr_(NULL) {}
-  explicit InternalMetadataWithArena(Arena* arena)
-      : ptr_ (arena) {}
+  explicit InternalMetadataWithArena(Arena* arena);
 
   ~InternalMetadataWithArena() {
     if (have_unknown_fields() && arena() == NULL) {