Clean up WebVR RequestPresent and make callback asynchronous.

chrome/browser/android/vr_shell/vr_shell_delegate.cc

Index: chrome/browser/android/vr_shell/vr_shell_delegate.cc
diff --git a/chrome/browser/android/vr_shell/vr_shell_delegate.cc b/chrome/browser/android/vr_shell/vr_shell_delegate.cc
index ae4acc523ce7317b1e0c39f8bad9a523af61170c..cffe81ba46bd5df71cf13784615fcdd040f03d20 100644
--- a/chrome/browser/android/vr_shell/vr_shell_delegate.cc
+++ b/chrome/browser/android/vr_shell/vr_shell_delegate.cc
@@ -67,17 +67,30 @@ void VrShellDelegate::ExitWebVRIfNecessary(JNIEnv* env, jobject obj) {
   device_provider_->OnGvrDelegateRemoved();
 }
 
-bool VrShellDelegate::RequestWebVRPresent(
-    base::WeakPtr<device::GvrDeviceProvider> device_provider) {
-  // Only set one device provider at a time
+void VrShellDelegate::SetPresentResult(JNIEnv* env, jobject obj,
+                                       jboolean result) {
+  CHECK(!present_callback_.is_null());
+  present_callback_.Run(result);
+  present_callback_.Reset();
+}
+
+void VrShellDelegate::RequestWebVRPresent(
+    base::WeakPtr<device::GvrDeviceProvider> device_provider,
+    const base::Callback<void(bool)>& callback) {
+  if (!present_callback_.is_null()) {
+    // Can only handle one request at a time. This is also extremely unlikely to
+    // happen in practice.
+    callback.Run(false);
+  }
+  // Only set one device provider at a time.
   DCHECK(!device_provider_);
+
   device_provider_ = device_provider;
+  present_callback_ = callback;
 
-  // If/When VRShell is ready for use it will call OnVrShellReady.
+  // If/When VRShell is ready for use it will call SetPresentResult.
   JNIEnv* env = AttachCurrentThread();
-  Java_VrShellDelegate_enterVRIfNecessary(env, j_vr_shell_delegate_.obj(),
-                                          true);
-  return true;
+  Java_VrShellDelegate_presentRequested(env, j_vr_shell_delegate_.obj(), true);
 }
 
 void VrShellDelegate::ExitWebVRPresent() {