GL: Temporarily disable parallel shader compile.

src/libANGLE/renderer/gl/RendererGL.cpp

@@ -566,6 +566,11 @@ angle::Result RendererGL::memoryBarrierByRegion(GLbitfield barriers)
 
 bool RendererGL::bindWorkerContext(std::string *infoLog)
 {
+    if (mWorkarounds.disableWorkerContexts)
+    {
+        return false;
+    }
+
     std::thread::id threadID = std::this_thread::get_id();
     std::lock_guard<std::mutex> lock(mWorkerMutex);
     std::unique_ptr<WorkerContext> workerContext;

src/libANGLE/renderer/gl/WorkaroundsGL.h

@@ -172,6 +172,10 @@ struct WorkaroundsGL
     // platforms.
     // http://anglebug.com/3045
     bool dontRelinkProgramsInParallel = false;
+
+    // Some tests have been seen to fail using worker contexts, this switch allows worker contexts
+    // to be disabled for some platforms. http://crbug.com/849576
+    bool disableWorkerContexts = false;
 };
 
 inline WorkaroundsGL::WorkaroundsGL() = default;

src/libANGLE/renderer/gl/renderergl_utils.cpp

@@ -1444,6 +1444,8 @@ void GenerateWorkarounds(const FunctionsGL *functions, WorkaroundsGL *workaround
     workarounds->queryCounterBitsGeneratesErrors = IsNexus5X(vendor, device);
 
     workarounds->dontRelinkProgramsInParallel = IsAndroid() || (IsWindows() && IsIntel(vendor));
+
+    workarounds->disableWorkerContexts = true;
 }
 
 void ApplyWorkarounds(const FunctionsGL *functions, gl::Workarounds *workarounds)