Test double indirect row_matrix access. (#3335)

Looking at the code in one of the backends I see this is problematic
so it seemed there should be a test.

Associated with https://crbug.com/angleproject/6386 .

Author: greggman

sdk/tests/conformance2/glsl3/matrix-row-major-dynamic-indexing.html

@@ -33,6 +33,22 @@
     my_FragColor = vec4(1.0 - f, f, 0.0, 1.0);
 }
 </script>
+<script id="fshaderRowMatrixIndexedByRowMatrixInUniformBlock" type="x-shader/x-fragment">#version 300 es
+precision mediump float;
+
+uniform Stuff {
+  layout(row_major) mat4 u_mat[3];
+  layout(row_major) mat4 u_ndx[3];
+} stuff;
+
+
+out vec4 my_FragColor;
+
+void main() {
+  vec4 row = stuff.u_mat[int(stuff.u_ndx[1][1][3])][2];
+  my_FragColor = row == vec4(9, 10, 11, 12) ? vec4(0, 1, 0, 1) : vec4(1, 0, 0, 1);
+}
+</script>
 <script type="application/javascript">
 "use strict";
 description("Indexing row-major matrices within a uniform block should work");
@@ -49,6 +65,51 @@
     0, 0, 0, 0,
     0, 0, 0, 0,
   ])}],
+},
+{
+  fShaderId: 'fshaderRowMatrixIndexedByRowMatrixInUniformBlock',
+  fShaderSuccess: true,
+  linkSuccess: true,
+  passMsg: '',
+  uniformBlocks: [{name: "Stuff", value: new Float32Array([
+    // mat4 u_mat[3]
+     1,  2,  3,  4,
+     5,  6,  7,  8,
+     9, 10, 11, 12,
+    13, 14, 15, 16,
+
+         //  +-- we should be pulling out this column
+         //  |
+         //  V
+     1,  5,  9, 13,
+     2,  6, 10, 14,
+     3,  7, 11, 15,
+     4,  8, 12, 16,
+
+     2, 10, 18, 22,
+     4, 12, 20, 28,
+     6, 14, 22, 30,
+     8, 16, 24, 32,
+
+    // mat4 u_ndx[3]
+    0, 0, 0, 0,
+    0, 0, 0, 0,
+    0, 0, 0, 0,
+    0, 0, 0, 0,
+
+    0, 0, 0, 0,
+    0, 0, 0, 2,
+    0, 0, 0, 0,
+    0, 1, 0, 0,
+    // ^
+    // |
+    // +-- we should be reading this value as an index into u_mat
+
+    0, 0, 0, 0,
+    0, 0, 0, 0,
+    0, 0, 0, 0,
+    0, 0, 0, 0,
+  ])}],
 }
 ], 2);
 </script>