Fix OnScreenKeyboard crash on windows ASAN debug build

Change Assert to STA from MTA. Add comment and bug describing that
WinRT use really should be in a MTA, but currently is on the UI thread
which is STA.

BUG=852317,852386

Change-Id: I3a284010638ae848b1e9b5ee6c92646a5a9a1dea
Reviewed-on: https://chromium-review.googlesource.com/1099184Reviewed-by: Robert Liao <robliao@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#566910}

ui/base/ime/win/on_screen_keyboard_display_manager_input_pane.cc

@@ -86,7 +86,10 @@ bool OnScreenKeyboardDisplayManagerInputPane::EnsureInputPanePointers() {
     return false;
   }
 
-  base::win::AssertComApartmentType(base::win::ComApartmentType::MTA);
+  // TODO(dtapuska): https://crbug.com/852386. Use TaskScheduler to access the
+  // WinRT APIs.
+  base::win::AssertComApartmentType(base::win::ComApartmentType::STA);
+
   base::win::ScopedHString input_pane_guid = base::win::ScopedHString::Create(
       RuntimeClass_Windows_UI_ViewManagement_InputPane);
   Microsoft::WRL::ComPtr<IInputPaneInterop> input_pane_interop;