GLES1: glMatrixMode

BUG=angleproject:2306

Change-Id: I83e15990c10d9354c2db00766ddc7b0ab960aa5c
Reviewed-on: https://chromium-review.googlesource.com/996019
Commit-Queue: Lingfeng Yang <lfy@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/libANGLE/Context.cpp b/src/libANGLE/Context.cpp
index a239260..5fbc18b 100644
--- a/src/libANGLE/Context.cpp
+++ b/src/libANGLE/Context.cpp
@@ -6872,6 +6872,10 @@
                 *type      = GL_FLOAT;
                 *numParams = 4;
                 return true;
+            case GL_MATRIX_MODE:
+                *type      = GL_INT;
+                *numParams = 1;
+                return true;
         }
     }