gpu: Fix deserialization error in ServiceFontManager.

We deserialize skia data while holding a lock, which we block on if
skia tries to delete a handle as this data is creating new entries in
the strike cache.

R=ericrk@chromium.org

Bug: 887422, 887152
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: Id32cb071834186e7de0dac16902c452c3ccdb102
Reviewed-on: https://chromium-review.googlesource.com/1236455Reviewed-by: Eric Karl <ericrk@chromium.org>
Commit-Queue: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592847}

gpu/command_buffer/service/service_font_manager.cc

@@ -171,8 +171,11 @@ bool ServiceFontManager::Deserialize(
   if (!deserializer.Read<uint64_t>(&skia_data_size))
     return false;
 
-  if (!deserializer.ReadStrikeData(strike_client_.get(), skia_data_size))
-    return false;
+  {
+    base::AutoUnlock release(lock_);
+    if (!deserializer.ReadStrikeData(strike_client_.get(), skia_data_size))
+      return false;
+  }
 
   return true;
 }