Fix blits from multisampled renderbuffers to alpha:false WebGL back buffer.

gpu/command_buffer/service/gles2_cmd_decoder_passthrough.cc

 // Copyright (c) 2016 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_passthrough.h"
 
 #include "base/strings/string_split.h"
 #include "gpu/command_buffer/service/feature_info.h"
 #include "gpu/command_buffer/service/gl_utils.h"
 #include "ui/gl/gl_version_info.h"
@@ skipping 867 matching lines @@
       glBindTexture(target, service_id);
     }
   }
 
   // Reset the active texture unit if it was changed
   if (cur_texture_unit != active_texture_unit_) {
     glActiveTexture(static_cast<GLenum>(GL_TEXTURE0 + active_texture_unit_));
   }
 }
 
+error::Error GLES2DecoderPassthroughImpl::BindTexImage2DCHROMIUMImpl(
+    GLenum target,
+    GLenum internalformat,
+    GLint imageId) {
+  if (target != GL_TEXTURE_2D) {
+    InsertError(GL_INVALID_ENUM, "Invalid target");
+    return error::kNoError;
+  }
+
+  gl::GLImage* image = image_manager_->LookupImage(imageId);
+  if (image == nullptr) {
+    InsertError(GL_INVALID_OPERATION, "No image found with the given ID");
+    return error::kNoError;
+  }
+
+  if (internalformat) {
+    if (!image->BindTexImageWithInternalformat(target, internalformat)) {
+      image->CopyTexImage(target);
+    }
+  } else {
+    if (!image->BindTexImage(target)) {
+      image->CopyTexImage(target);
+    }
+  }
+
+  return error::kNoError;
+}
+
 #define GLES2_CMD_OP(name)                                               \
   {                                                                      \
       &GLES2DecoderPassthroughImpl::Handle##name, cmds::name::kArgFlags, \
       cmds::name::cmd_flags,                                             \
       sizeof(cmds::name) / sizeof(CommandBufferEntry) - 1,               \
   }, /* NOLINT */
 
 const GLES2DecoderPassthroughImpl::CommandInfo
     GLES2DecoderPassthroughImpl::command_info[] = {
         GLES2_COMMAND_LIST(GLES2_CMD_OP)};
 
 #undef GLES2_CMD_OP
 
 }  // namespace gles2
 }  // namespace gpu