Add files for libexif GN target.

third_party/libexif/BUILD.gn

+# Copyright 2015 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# Linux should use system libexif
+if (!is_linux || is_chromeos) {
+
+  # TODO(thestig): Properly support building on Linux.
+  config("libexif_config") {
+    include_dirs = [ "sources" ]
+  }
+
+  static_library("libexif") {

[Nico, 2015/09/02 22:54:49]

doesn't this have to be a dll? image_metadata_extractor.cc is trying to load
libexif.dll...

[Slava Chigrin, 2015/09/03 19:28:17]

Yes, my bad. In GYP it defined ad "loadable_module", I will make fix soon. Sorry
for this mistake...

+    sources = [
+      "sources/libexif/exif-byte-order.c",
+      "sources/libexif/exif-content.c",
+      "sources/libexif/exif-data.c",
+      "sources/libexif/exif-entry.c",
+      "sources/libexif/exif-format.c",
+      "sources/libexif/exif-ifd.c",
+      "sources/libexif/exif-loader.c",
+      "sources/libexif/exif-log.c",
+      "sources/libexif/exif-mem.c",
+      "sources/libexif/exif-mnote-data.c",
+      "sources/libexif/exif-tag.c",
+      "sources/libexif/exif-utils.c",
+      "sources/libexif/canon/exif-mnote-data-canon.c",
+      "sources/libexif/canon/mnote-canon-entry.c",
+      "sources/libexif/canon/mnote-canon-tag.c",
+      "sources/libexif/fuji/exif-mnote-data-fuji.c",
+      "sources/libexif/fuji/mnote-fuji-entry.c",
+      "sources/libexif/fuji/mnote-fuji-tag.c",
+      "sources/libexif/olympus/exif-mnote-data-olympus.c",
+      "sources/libexif/olympus/mnote-olympus-entry.c",
+      "sources/libexif/olympus/mnote-olympus-tag.c",
+      "sources/libexif/pentax/exif-mnote-data-pentax.c",
+      "sources/libexif/pentax/mnote-pentax-entry.c",
+      "sources/libexif/pentax/mnote-pentax-tag.c",
+    ]
+
+    include_dirs = [ "sources" ]
+
+    # TODO(GYP): Additional options for non-Windows platforms.
+
+    if (is_win) {
+      defines = [
+        # This seems like a hack, but this is what WebKit Win does.
+        "snprintf=_snprintf",
+        "inline=__inline",
+      ]
+
+      ldflags = [ "/DEF:" + rebase_path("libexif.def") ]
+
+      cflags = [
+        "/wd4018",  # size/unsigned mismatch
+        "/wd4267",  # size_t -> ExifLong truncation on amd64
+      ]
+
+      # TODO(GYP): Handle /analyze switch, when it will be used in GN.
+    }
+
+    configs -= [ "//build/config/compiler:chromium_code" ]
+    configs += [ "//build/config/compiler:no_chromium_code" ]
+
+    public_configs = [ ":libexif_config" ]
+  }
+}