Add SkWebpCodec, for decoding .webp images.

dm/DM.cpp

Index: dm/DM.cpp
diff --git a/dm/DM.cpp b/dm/DM.cpp
index 33ce0a41bff68288ac16736fce3fa1fc87ac438b..60929d57008eadcf1b272885e73c2c7ad888ec93 100644
--- a/dm/DM.cpp
+++ b/dm/DM.cpp
@@ -259,8 +259,8 @@ static bool codec_supported(const char* ext) {
     // FIXME: Once other versions of SkCodec are available, we can add them to this
     // list (and eventually we can remove this check once they are all supported).
     static const char* const exts[] = {
-        "bmp", "gif", "jpg", "jpeg", "png", "ico", "wbmp",
-        "BMP", "GIF", "JPG", "JPEG", "PNG", "ICO", "WBMP"
+        "bmp", "gif", "jpg", "jpeg", "png", "ico", "wbmp", "webp",
+        "BMP", "GIF", "JPG", "JPEG", "PNG", "ICO", "WBMP", "WEBP",
     };
 
     for (uint32_t i = 0; i < SK_ARRAY_COUNT(exts); i++) {