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

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 3491223854744ffe23d1136248aabeb49e2ca252..96d0a336604771df8cd9e843565dbf37c615601e 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -15096,22 +15096,18 @@ void GLES2DecoderImpl::TexStorageImpl(GLenum target,
     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);