Reset GLManager so it can be reused with ES2 context

Problem: When the GLVirtualContextsTest tests are run on a device with
Open GL ES 2.0, the tests fail during initialization because it tries
to re-initialize a GLManager (gl_real_) after failing to initialize as
content type ES 3.0. The problem being theat the gl_real_ is now in
an inconsistent state and cannot be initialized again.

Solution: Reset the GLManager (gl_real_) after failing to be
initialized as ES3, so that it can be re-tried as ES2.

Bug: None
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;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: Idb0a6947baa80c3135418504e77458171eebe1fa
Reviewed-on: https://chromium-review.googlesource.com/999268Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: Antoine Labour <piman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548838}

gpu/command_buffer/tests/gl_manager.cc

@@ -603,4 +603,9 @@ void GLManager::SetSnapshotRequested() {}
 ContextType GLManager::GetContextType() const {
   return context_type_;
 }
+
+void GLManager::Reset() {
+  Destroy();
+  SetupBaseContext();
+}
 }  // namespace gpu

gpu/command_buffer/tests/gl_manager.h

@@ -163,6 +163,8 @@ class GLManager : private GpuControl {
   size_t GetSharedMemoryBytesAllocated() const;
   ContextType GetContextType() const;
 
+  void Reset();
+
  private:
   void SetupBaseContext();
 

gpu/command_buffer/tests/gl_virtual_contexts_unittest.cc

@@ -33,6 +33,7 @@ class GLVirtualContextsTest
     // If the gl_real context is not initialised, switch to ES2 context type
     // and re-initialise
     if (!gl_real_.IsInitialized()) {
+      gl_real_.Reset();  // Must reset object before initializing again
       options.context_type = CONTEXT_TYPE_OPENGLES2;
       gl_real_.InitializeWithWorkarounds(options, workarounds);
     }