Initialize remaining passthrough command decoder caps.

gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc b/gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc
index 3a884f4401a17b95ff85f91fabad43b17e0b7f7e..57cfae7469696ca6c5f55e64929ec60ac4e90f16 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc
@@ -3322,6 +3322,17 @@ error::Error GLES2DecoderPassthroughImpl::DoPostSubBufferCHROMIUM(
     GLint y,
     GLint width,
     GLint height) {
+  if (!surface_->SupportsPostSubBuffer()) {
+    InsertError(GL_INVALID_OPERATION,
+                "glPostSubBufferCHROMIUM is not supported for this surface.");
+    return error::kNoError;
+  }
+
+  gfx::SwapResult result = surface_->PostSubBuffer(x, y, width, height);
+  if (result == gfx::SwapResult::SWAP_FAILED) {
+    LOG(ERROR) << "Context lost because PostSubBuffer failed.";
+  }
+  // TODO(geofflang): force the context loss?
   return error::kNoError;
 }