Add PinUser32() to wWinMain for Content_Shell.exe

Calls to pin or load user32.dll cannot happen on the main thread loop
because they are blocking calls. The test code always executes on the
main thread loop, so if the test code hits anything that requires
user32 then it will crash (with dchecks on). To avoid this, we simply
call PinUser32() in wWinMain before we get to the main thread loop.
This same thing is done in browser_tests_main.cc.

Bug: 962559
Change-Id: I82b4e7a41117db77e2ff3a01314cb9e82c7b1b8f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1617911Reviewed-by: Peter Beverloo <peter@chromium.org>
Commit-Queue: Cliff Smolinsky <cliffsmo@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#661391}

content/shell/app/shell_main.cc

@@ -7,6 +7,7 @@
 #include "content/shell/app/shell_main_delegate.h"
 
 #if defined(OS_WIN)
+#include "base/win/win_util.h"
 #include "content/public/app/sandbox_helper_win.h"
 #include "sandbox/win/src/sandbox_types.h"
 #endif
@@ -19,6 +20,9 @@ int APIENTRY wWinMain(HINSTANCE instance, HINSTANCE, wchar_t*, int) {
 int main() {
   HINSTANCE instance = GetModuleHandle(NULL);
 #endif
+  // Load and pin user32.dll to avoid having to load it once tests start while
+  // on the main thread loop where blocking calls are disallowed.
+  base::win::PinUser32();
   sandbox::SandboxInterfaceInfo sandbox_info = {0};
   content::InitializeSandboxInfo(&sandbox_info);
   content::ShellMainDelegate delegate;