Add an EGL_ANGLE_surface_orientation extension.

BUG=angleproject:1262

Change-Id: Ifbb0f5302311a68a0c6f02baaea706cbb7055a52
Reviewed-on: https://chromium-review.googlesource.com/320011
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/Config.cpp b/src/libANGLE/Config.cpp
index c558b31..d511df3 100644
--- a/src/libANGLE/Config.cpp
+++ b/src/libANGLE/Config.cpp
@@ -57,7 +57,8 @@
       transparentType(EGL_NONE),
       transparentRedValue(0),
       transparentGreenValue(0),
-      transparentBlueValue(0)
+      transparentBlueValue(0),
+      optimalOrientation(0)
 {
 }
 
@@ -251,6 +252,9 @@
               case EGL_MAX_PBUFFER_WIDTH:         match = config.maxPBufferWidth >= attributeValue;                   break;
               case EGL_MAX_PBUFFER_HEIGHT:        match = config.maxPBufferHeight >= attributeValue;                  break;
               case EGL_MAX_PBUFFER_PIXELS:        match = config.maxPBufferPixels >= attributeValue;                  break;
+              case EGL_OPTIMAL_SURFACE_ORIENTATION_ANGLE:
+                  match = config.optimalOrientation == attributeValue;
+                  break;
               default: UNREACHABLE();
             }