gpu: Clarify sized texture format is available only if ES3 context or immutable texture is supported

gpu/command_buffer/service/gles2_cmd_decoder.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 "gpu/command_buffer/service/gles2_cmd_decoder.h"
 
 #include <limits.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
@@ skipping 15078 matching lines @@
   if (dimension == ContextState::k2D) {
     glTexStorage2DEXT(target, levels, internal_format, width, height);
   } else {
     glTexStorage3D(target, levels, internal_format, width, height, depth);
   }
 
   {
     GLsizei level_width = width;
     GLsizei level_height = height;
     GLsizei level_depth = depth;
-    GLenum adjusted_format =
-        feature_info_->IsES3Enabled() ? internal_format : format;

[dshwang, 2016/10/10 15:45:49]

Remove this hack.

Rationale
1. After ES3 support, gles2 decoder can handle both unsized format as well as
sized format.
2. many gl2 extensions support sized format
3. texImage2D already handles sized format in es2
4. CMAA needs to know exact internal format
https://cs.chromium.org/chromium/src/gpu/command_buffer/service/gles2_cmd_app...

     for (int ii = 0; ii < levels; ++ii) {
       if (target == GL_TEXTURE_CUBE_MAP) {
         for (int jj = 0; jj < 6; ++jj) {
           GLenum face = GL_TEXTURE_CUBE_MAP_POSITIVE_X + jj;
-          texture_manager()->SetLevelInfo(texture_ref, face, ii,
-                                          adjusted_format,
-                                          level_width, level_height, 1,
-                                          0, format, type, gfx::Rect());
+          texture_manager()->SetLevelInfo(
+              texture_ref, face, ii, internal_format, level_width, level_height,
+              1, 0, format, type, gfx::Rect());
         }
       } else {
-        texture_manager()->SetLevelInfo(texture_ref, target, ii,
-                                        adjusted_format,
-                                        level_width, level_height, level_depth,
-                                        0, format, type, gfx::Rect());
+        texture_manager()->SetLevelInfo(
+            texture_ref, target, ii, internal_format, level_width, level_height,
+            level_depth, 0, format, type, gfx::Rect());
       }
       level_width = std::max(1, level_width >> 1);
       level_height = std::max(1, level_height >> 1);
       if (target == GL_TEXTURE_3D)
         level_depth = std::max(1, level_depth >> 1);
     }
     texture->SetImmutable(true);
   }
 }
 
@@ skipping 1966 matching lines @@
 }
 
 // Include the auto-generated part of this file. We split this because it means
 // we can easily edit the non-auto generated parts right here in this file
 // instead of having to edit some template or the code generator.
 #include "base/macros.h"
 #include "gpu/command_buffer/service/gles2_cmd_decoder_autogen.h"
 
 }  // namespace gles2
 }  // namespace gpu