re-enable depth texture gl test

gpu/command_buffer/tests/gl_depth_texture_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <GLES2/gl2.h>
 #include <GLES2/gl2ext.h>
 
 #include "gpu/command_buffer/tests/gl_manager.h"
 #include "gpu/command_buffer/tests/gl_test_utils.h"
 #include "testing/gmock/include/gmock/gmock.h"
@@ skipping 42 matching lines @@
 
 namespace {
 
 struct FormatType {
   GLenum format;
   GLenum type;
 };
 
 }  // anonymous namespace
 
-// Temporarily marked disabled due to failure on gpu bots.
-// https://code.google.com/p/chromium/issues/detail?id=135229
-TEST_F(DepthTextureTest, DISABLED_RenderTo) {
+TEST_F(DepthTextureTest, RenderTo) {
   if (!GLTestHelper::HasExtension("GL_CHROMIUM_depth_texture")) {
     return;
   }
 
   bool have_depth_stencil = GLTestHelper::HasExtension(
       "GL_OES_packed_depth_stencil");
 
   static const char* v_shader_str = SHADER(
       attribute vec4 v_position;
       void main()
@@ skipping 106 matching lines @@
 
         EXPECT_EQ(actual[0], actual[1]);
         EXPECT_EQ(actual[1], actual[2]);
 
         if (xx > 0) {
           EXPECT_GT(actual[0], left[0]);
         }
         if (yy > 0) {
           EXPECT_GT(actual[0], down[0]);
         }
+
+        EXPECT_TRUE(actual[3] == actual[0] || actual[3] == 0xFF);
       }
     }
 
     // Check that bottom left corner is vastly different thatn top right.
     EXPECT_GT(
         actual_pixels[(kResolution * kResolution - 1) * 4] - actual_pixels[0],
         0xC0);
     GLTestHelper::CheckGLError("no errors", __LINE__);
   }
 }
 
 }  // namespace gpu