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 03f41575f6e154b0a1e853a73ca5983c1b263544..4a4846bd55b54993ee09dcb0aeabfdd4d3c1bb88 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -16141,22 +16141,18 @@ 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 20:57:10]

Here is inside GLES2DecoderImpl::TexStorageImpl().

texture_manager()->SetLevelInfo() checks if the sized format is registered in
|texture_sized_xxx_internal_format|

     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);