Don't require GL_ARB_gpu_shader5 in order to support ES 3.0.

ui/gl/gl_version_info.cc

 // Copyright 2014 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 "ui/gl/gl_version_info.h"
 
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_tokenizer.h"
 #include "base/strings/string_util.h"
@@ skipping 72 matching lines @@
     return true;
   }
 
   // Don't try supporting ES3 on ES2, or desktop before 3.3.
   if (is_es || !IsAtLeastGL(3, 3)) {
     return false;
   }
 
   bool has_transform_feedback =
       (IsAtLeastGL(4, 0) || has_extension("GL_ARB_transform_feedback2"));
-  bool has_sampler_indexing =
-      (IsAtLeastGL(4, 0) || has_extension("GL_ARB_gpu_shader5"));
+
+  // This code used to require the GL_ARB_gpu_shader5 extension in order to
+  // have support for dynamic indexing of sampler arrays, which was
+  // optionally supported in ESSL 1.00. However, since this is expressly
+  // forbidden in ESSL 3.00, and some desktop drivers (specifically
+  // Mesa/Gallium on AMD GPUs) don't support it, we no longer require it.
+
   // tex storage is available in core spec since GL 4.2.
   bool has_tex_storage = has_extension("GL_ARB_texture_storage");
 
   // TODO(cwallez) check for texture related extensions. See crbug.com/623577
 
-  return (has_transform_feedback &&
-          has_sampler_indexing &&
-          has_tex_storage);
+  return (has_transform_feedback && has_tex_storage);
 }
 
 void GLVersionInfo::ParseVersionString(const char* version_str,
                                        unsigned* major_version,
                                        unsigned* minor_version,
                                        bool* is_es,
                                        bool* is_es2,
                                        bool* is_es3) {
   // Make sure the outputs are always initialized.
   *major_version = 0;
@@ skipping 18 matching lines @@
     }
   }
   if (*is_es && *major_version == 2)
     *is_es2 = true;
   if (*is_es && *major_version == 3)
     *is_es3 = true;
   DCHECK(major_version != 0);
 }
 
 }  // namespace gl