VP8: disallow thread count changes

Currently allocations are done at encoder creation time. Going from
threaded to non-threaded would cause a crash.

Bug: chromium:1486441
Change-Id: Ie301c2a70847dff2f0daae408fbef1e4d42e73d4
(cherry picked from commit 3fbd1dc)

test/encode_api_test.cc

@@ -366,10 +366,6 @@ TEST(EncodeAPI, ConfigResizeChangeThreadCount) {
 
   for (const auto *iface : kCodecIfaces) {
     SCOPED_TRACE(vpx_codec_iface_name(iface));
-    if (!IsVP9(iface)) {
-      GTEST_SKIP() << "TODO(https://crbug.com/1486441) remove this condition "
-                      "after VP8 is fixed.";
-    }
     for (int i = 0; i < (IsVP9(iface) ? 2 : 1); ++i) {
       vpx_codec_enc_cfg_t cfg = {};
       struct Encoder {

vp8/encoder/onyx_if.c

@@ -1443,6 +1443,11 @@ void vp8_change_config(VP8_COMP *cpi, VP8_CONFIG *oxcf) {
   last_h = cpi->oxcf.Height;
   prev_number_of_layers = cpi->oxcf.number_of_layers;
 
+  if (cpi->initial_width) {
+    // TODO(https://crbug.com/1486441): Allow changing thread counts; the
+    // allocation is done once in vp8_create_compressor().
+    oxcf->multi_threaded = cpi->oxcf.multi_threaded;
+  }
   cpi->oxcf = *oxcf;
 
   switch (cpi->oxcf.Mode) {