VrShell: Exit fullscreen on app button press.

chrome/browser/android/vr_shell/vr_shell.cc

Index: chrome/browser/android/vr_shell/vr_shell.cc
diff --git a/chrome/browser/android/vr_shell/vr_shell.cc b/chrome/browser/android/vr_shell/vr_shell.cc
index a726bc4f4120060b0324ee8f1cc000e5acef0ea8..f3893bc3971a9ed43a0422d3e5e5abbf096f84d6 100644
--- a/chrome/browser/android/vr_shell/vr_shell.cc
+++ b/chrome/browser/android/vr_shell/vr_shell.cc
@@ -492,6 +492,12 @@ void VrShell::ForceExitVr() {
   Java_VrShellImpl_forceExitVr(env, j_vr_shell_.obj());
 }
 
+void VrShell::ExitFullscreen() {
+  if (web_contents_ && web_contents_->IsFullscreen()) {
+    web_contents_->ExitFullscreen(false);
+  }
+}
+
 void VrShell::OnVRVsyncProviderRequest(
     device::mojom::VRVSyncProviderRequest request) {
   PostToGlThreadWhenReady(base::Bind(&VrShellGl::OnRequest,