Enable accelerated WebKit compositor for Aura.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 7635514e3a95b38e80e1719b2e9f74961536d5e9..512c8e9d3f10677d7fc363b77b9f663e27ce5603 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -327,6 +327,14 @@
           'proprietary_codecs%': 1,
           'enable_webrtc%': 0,
         }],
+
+        # Use GPU accelerated cross process image transport by default
+        # on TOUCH_UI and linux builds with the Aura window manager
+        ['views_compositor==1 and OS=="linux"', {
+          'views_gpu_image_transport%': 1,
+        }, {
+          'views_gpu_image_transport%': 0,
+        }],
       ],
     },
 
@@ -339,6 +347,7 @@
     'toolkit_views%': '<(toolkit_views)',
     'use_only_pure_views%': '<(use_only_pure_views)',
     'views_compositor%': '<(views_compositor)',
+    'views_gpu_image_transport%': '<(views_gpu_image_transport)',
     'use_aura%': '<(use_aura)',
     'use_openssl%': '<(use_openssl)',
     'use_nss%': '<(use_nss)',
@@ -937,6 +946,9 @@
       ['views_compositor==1', {
         'defines': ['VIEWS_COMPOSITOR=1'],
       }],
+      ['views_gpu_image_transport==1', {
+        'defines': ['UI_COMPOSITOR_IMAGE_TRANSPORT'],
+      }],
       ['use_aura==1', {
         'defines': ['USE_AURA=1'],
       }],