Enable Chromium clang style plugin for libANGLE.

This fixes a few style warnings:

 * auto should not deduce to raw pointer type
 * inlined virtual methods are not allowed
 * non-trivial constructors and destructors should be explicit
 * inlined non-trivial constructors should not be in-class
 * missing override keywords

Bug: angleproject:3069
Change-Id: I3b3e55683691da3ebf6da06a5d3c729c71b6ee53
Reviewed-on: https://chromium-review.googlesource.com/c/1407640
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
diff --git a/src/libANGLE/Image.cpp b/src/libANGLE/Image.cpp
index bcf64a8..9305041 100644
--- a/src/libANGLE/Image.cpp
+++ b/src/libANGLE/Image.cpp
@@ -137,6 +137,8 @@
     : mImplementation(factory->createExternalImageSibling(context, target, buffer, attribs))
 {}
 
+ExternalImageSibling::~ExternalImageSibling() = default;
+
 gl::Extents ExternalImageSibling::getAttachmentSize(const gl::ImageIndex &imageIndex) const
 {
     return mImplementation->getSize();