Bug 1186229 - Enable Gtk+3 builds by default. r=gps

Note Gtk+3 builds need both Gtk+2 *and* Gtk+3.

configure.in

@@ -1042,7 +1042,7 @@ MOZ_FS_LAYOUT=unix
 
 USE_DEPENDENT_LIBS=1
 
-_PLATFORM_DEFAULT_TOOLKIT=cairo-gtk2
+_PLATFORM_DEFAULT_TOOLKIT=cairo-gtk3
 
 if test -n "$CROSS_COMPILE"; then
     OS_TARGET="${target_os}"

python/mozboot/mozboot/archlinux.py

@@ -30,6 +30,7 @@ class ArchlinuxBootstrapper(BaseBootstrapper):
         'dbus-glib',
         'desktop-file-utils',
         'gtk2',
+        'gtk3',
         'hicolor-icon-theme',
         'hunspell',
         'icu',

python/mozboot/mozboot/centos.py

@@ -39,6 +39,7 @@ class CentOSBootstrapper(BaseBootstrapper):
             'gstreamer-devel',
             'gstreamer-plugins-base-devel',
             'gtk2-devel',
+            'gtk3-devel',
             'libstdc++-static',
             'libXt-devel',
             'mesa-libGL-devel',

python/mozboot/mozboot/debian.py

@@ -37,6 +37,7 @@ class DebianBootstrapper(BaseBootstrapper):
         'libgstreamer0.10-dev',
         'libgstreamer-plugins-base0.10-dev',
         'libgtk2.0-dev',
+        'libgtk-3-dev',
         'libiw-dev',
         'libnotify-dev',
         'libpulse-dev',

python/mozboot/mozboot/fedora.py

@@ -33,6 +33,8 @@ class FedoraBootstrapper(BaseBootstrapper):
             'glibc-static',
             'gstreamer-devel',
             'gstreamer-plugins-base-devel',
+            'gtk2-devel',  # it's optional in Fedora 20's GNOME Software
+                           # Development group.
             'libstdc++-static',
             'libXt-devel',
             'mesa-libGL-devel',

python/mozboot/mozboot/freebsd.py

@@ -23,6 +23,7 @@ class FreeBSDBootstrapper(BaseBootstrapper):
             'dbus-glib',
             'gstreamer-plugins',
             'gtk2',
+            'gtk3',
             'libGL',
             'pulseaudio',
             'v4l_compat',

python/mozboot/mozboot/gentoo.py

@@ -17,6 +17,7 @@ class GentooBootstrapper(BaseBootstrapper):
 
     def install_browser_packages(self):
         self.run_as_root(['emerge', '--onlydeps', '--quiet', 'firefox'])
+        self.run_as_root(['emerge', '--quiet', 'gtk+'])
 
     def _update_package_manager(self):
         self.run_as_root(['emerge', '--sync'])

python/mozboot/mozboot/openbsd.py

@@ -23,6 +23,7 @@ class OpenBSDBootstrapper(BaseBootstrapper):
             'llvm',
             'yasm',
             'gtk+2',
+            'gtk+3',
             'dbus-glib',
             'gstreamer-plugins-base',
             'pulseaudio',