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

gpu/command_buffer/service/gles2_cmd_decoder_passthrough.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder_passthrough.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder_passthrough.cc b/gpu/command_buffer/service/gles2_cmd_decoder_passthrough.cc
index eac5a98899c05e024437b08b58350db93e6b14bd..032369e06db46d17aa9dc61a7f5f377dc5fcdf2d 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder_passthrough.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder_passthrough.cc
@@ -885,6 +885,34 @@ void GLES2DecoderPassthroughImpl::UpdateTextureBinding(GLenum target,
   }
 }
 
+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, \