Implement the CPU fallback for CopyTextureCHROMIUM on OpenGL.

BUG=angleproject:1932

Change-Id: Iabc1a3e361d66313dc16bf19b392402b7836f8a5
Reviewed-on: https://chromium-review.googlesource.com/612562
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/common/angleutils.h b/src/common/angleutils.h
index 7fd346d..809ddea 100644
--- a/src/common/angleutils.h
+++ b/src/common/angleutils.h
@@ -236,6 +236,7 @@
 #define snprintf _snprintf
 #endif
 
+#define GL_BGRX8_ANGLEX 0x6ABA
 #define GL_BGR565_ANGLEX 0x6ABB
 #define GL_BGRA4_ANGLEX 0x6ABC
 #define GL_BGR5_A1_ANGLEX 0x6ABD