Cherry-pick: [Android WebView] Fix in-line video part 1

Cherry-pick of Chromium crrev.com/r234924

BUG: 11706189

Original description:

Previously, TryCreateStreamTextureFactory was assuming that
GetOffscreenContextProviderForMainThread is already called. This is no
longer true after the refactoring in crrev.com/r232936.

Stop making this assumption and actually call
GetOffscreenContextProviderForMainThread instead.

Change-Id: Ic559c92d28494213d99db731bb6b2a42c2e60e18
diff --git a/content/browser/android/in_process/synchronous_compositor_impl.cc b/content/browser/android/in_process/synchronous_compositor_impl.cc
index aa34ba4..c354085 100644
--- a/content/browser/android/in_process/synchronous_compositor_impl.cc
+++ b/content/browser/android/in_process/synchronous_compositor_impl.cc
@@ -250,7 +250,9 @@
 SynchronousCompositorFactoryImpl::TryCreateStreamTextureFactory() {
   scoped_refptr<StreamTextureFactorySynchronousImpl::ContextProvider>
       context_provider;
-  if (CanCreateMainThreadContext() && offscreen_context_for_main_thread_) {
+  if (CanCreateMainThreadContext() &&
+      GetOffscreenContextProviderForMainThread()) {
+    DCHECK(offscreen_context_for_main_thread_);
     DCHECK(wrapped_gl_context_for_main_thread_);
     context_provider =
         new VideoContextProvider(offscreen_context_for_main_thread_,