Quick and dirty "how to try this" recipe
________________________________________

First, save this patch as

	/tmp/chromium-ebuild-widevine.patch

Set the widevine useflag as you want it in /etc/portage/make.conf (or wherever).
	
now, as root, run the something like the following sequence of commands in bash
(warning: the following is untested, and unlikely to be 100% bug-free, so don't
just copy-paste all this wholesale!):

_GX86=$( portageq get_repo_path / gentoo )
_OVL=${_GX86}
# (better) alternative: set _OVL to the location of your favorite overlay

# if overlay != gx86, copy everything over from www-plugins/chrome-binary-plugins
# and www-client/chromium (shouldn't overwrite any existing files).
if [[ ${_GX86} != ${_OVL} ]]; then
	mkdir -p ${_OVL}/www-plugins
	cp -nrv ${_GX86}/www-plugins/chrome-binary-plugins ${_OVL}/www-plugins/
	mkdir -p ${_OVL}/www-client
	cp -nrv ${_GX86}/www-client/chromium ${_OVL}/www-client/
fi

# identify best gx86 ebuilds to use as basis
_chrome_binary_plugins=$( portageq pquery www-plugins/chrome-binary-plugins:beta::gentoo | tail -n 1)
_chrome_binary_plugins="${_GX86}/www-plugins/chrome-binary-plugins/${_chrome_binary_plugins#www-plugins/}.ebuild"
_chromium=$( portageq pquery '=www-client/chromium-44*::gentoo' | tail -n 1 )
_chromium="${_GX86}/www-client/chromium/${_chromium#www-client/}.ebuild"

# revbump/upgrade chrome-binary-plugins
cd "${_OVL}/www-plugins/chrome-binary-plugins"
cp -v "${_chrome_binary_plugins}" ./chrome-binary-plugins-44.0.2403.61_beta1.ebuild
ebuild chrome-binary-plugins-44.0.2403.61_beta1.ebuild digest clean merge

# revbump/patch chromium ebuild
cd "${_OVL}/www-client/chromium"
cp -v "${_chromium}" ./chromium-44.0.2403.61.ebuild
patch -p1 < /tmp/chromium-ebuild-widevine.patch
ebuild chromium-44.0.2403.61.ebuild digest 

# build it
ebuild chromium-44.0.2403.61.ebuild clean install

# wait ... for ... it ... 

# merge (optional)
ebuild chromium-44.0.2403.61.ebuild merge

--- a/chromium-44.0.2403.61.ebuild	2015-06-08 19:17:33.000000000 -0700
+++ b/chromium-44.0.2403.61.ebuild	2015-06-24 20:15:58.726368209 -0700
@@ -1,6 +1,6 @@
 # Copyright 1999-2015 Gentoo Foundation
 # Distributed under the terms of the GNU General Public License v2
-# $Header: /var/cvsroot/gentoo-x86/www-client/chromium/chromium-44.0.2403.30.ebuild,v 1.1 2015/06/09 02:17:33 floppym Exp $
+# $Header: $
 
 EAPI="5"
 PYTHON_COMPAT=( python2_7 )
@@ -19,7 +19,7 @@ SRC_URI="https://commondatastorage.googl
 LICENSE="BSD"
 SLOT="0"
 KEYWORDS="~amd64 ~arm ~x86"
-IUSE="cups gnome gnome-keyring hidpi kerberos neon pic +proprietary-codecs pulseaudio selinux +tcmalloc"
+IUSE="cups gnome gnome-keyring hidpi kerberos neon pic +proprietary-codecs pulseaudio selinux +tcmalloc +widevine"
 RESTRICT="proprietary-codecs? ( bindist )"
 
 # Native Client binaries are compiled with different set of flags, bug #452066.
@@ -91,7 +91,8 @@ DEPEND="${RDEPEND}
 	sys-apps/hwids[usb(+)]
 	>=sys-devel/bison-2.4.3
 	sys-devel/flex
-	virtual/pkgconfig"
+	virtual/pkgconfig
+	widevine? ( www-plugins/chrome-binary-plugins[widevine] )"
 
 # For nvidia-drivers blocker, see bug #413637 .
 RDEPEND+="
@@ -188,6 +189,19 @@ src_prepare() {
 
 	epatch "${FILESDIR}/${PN}-system-jinja-r7.patch"
 
+	if use widevine; then
+		local WIDEVINE_VERSION="$(< "${ROOT}/usr/$(get_libdir)/chromium-browser/widevine.version")"
+		[[ -z $WIDEVINE_VERSION ]] && die "Could not determine Widevine version."
+		local sedscript='$i#include "third_party/widevine/cdm/widevine_cdm_common.h"\n'
+		sedscript+='#define WIDEVINE_CDM_AVAILABLE\n'
+		sedscript+="#define WIDEVINE_CDM_VERSION_STRING \"${WIDEVINE_VERSION}\"\\n"
+		sed -e "${sedscript}" -i third_party/widevine/cdm/widevine_cdm_version.h || die
+
+		# build widevine_cdm but skip the license-server test
+		sed -e '1,/widevine_test_license_server/ s/"Chrome"/"Chromium"/g' \
+			-i third_party/widevine/cdm/widevine_cdm.gyp || die
+	fi
+
 	epatch_user
 
 	# Remove most bundled libraries. Some are still needed.
@@ -285,10 +299,23 @@ src_prepare() {
 		'v8/src/third_party/fdlibm' \
 		'v8/src/third_party/kernel' \
 		'v8/src/third_party/valgrind' \
+		'third_party/devscripts' \
 		--do-remove || die
 }
 
 src_configure() {
+
+	if use widevine; then
+		local WIDEVINE_SUPPORTED_ARCHS="x64 ia32"
+		local arch
+		for arch in $WIDEVINE_SUPPORTED_ARCHS; do
+			mkdir -p third_party/widevine/cdm/linux/$arch
+			cp "${ROOT}/usr/$(get_libdir)/chromium-browser/libwidevinecdm.so" \
+				third_party/widevine/cdm/widevine_cdm_*.h \
+				third_party/widevine/cdm/linux/$arch/ \
+					|| die "Could not copy headers for Widevine."
+		done
+	fi
 	local myconf=""
 
 	# Never tell the build system to "enable" SSE2, it has a few unexpected
@@ -580,7 +607,9 @@ src_install() {
 	newman out/Release/chrome.1 chromium${CHROMIUM_SUFFIX}.1 || die
 	newman out/Release/chrome.1 chromium-browser${CHROMIUM_SUFFIX}.1 || die
 
-	doexe out/Release/libffmpegsumo.so || die
+	if use widevine; then
+		doexe out/Release/libwidevinecdmadapter.so || die
+	fi
 
 	# Install icons and desktop entry.
 	local branding size