CHR-6375: [Windows] Fixed crash on fallback from ANGLE to SwiftShader.

During fallback from ANGLE to SwiftShader it is required to unload
ANGLE libraries, otherwise SwiftShader will fail to load its own
libGLESv2.dll.

Fixed ANGLE platform reset.

Bug: 760063
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I02280b2c1cd6c3d81087c7e2befb412bb2a89510
Reviewed-on: https://chromium-review.googlesource.com/640992
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Cr-Commit-Position: refs/heads/master@{#499529}

ui/gl/angle_platform_impl.cc

@@ -193,6 +193,7 @@ void ResetPlatform(EGLDisplay display) {
     return;
   g_angle_reset_platform(static_cast<EGLDisplayType>(display));
   ResetCacheProgramCallback();
+  g_angle_reset_platform = nullptr;
 }
 
 void SetCacheProgramCallback(CacheProgramCallback callback) {

ui/gl/gl_implementation.cc

@@ -47,9 +47,20 @@ GLGetProcAddressProc g_get_proc_address;
 
 void CleanupNativeLibraries(void* unused) {
   if (g_libraries) {
-    // We do not call base::UnloadNativeLibrary() for these libraries as
-    // unloading libGL without closing X display is not allowed. See
-    // crbug.com/250813 for details.
+    bool unload_libraries = true;
+#if defined(USE_X11)
+    // We do not call base::UnloadNativeLibrary() for kGLImplementationDesktopGL
+    // which use libGL which unloading without closing X display is not allowed.
+    // See crbug.com/250813 for details.
+    // If kGLImplementationDesktopGL is used with switch "test-gl-lib" and ANGLE
+    // implementation then in case of fallback to SwiftShader crash will occur
+    // See crbug.com/760063 for details.
+    unload_libraries = GetGLImplementation() != kGLImplementationDesktopGL;
+#endif
+    if (unload_libraries) {
+      for (auto* library : *g_libraries)
+        base::UnloadNativeLibrary(library);
+    }
     delete g_libraries;
     g_libraries = NULL;
   }