Enable WebVR presentation from Chrome Custom Tab

chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrProxyActivity.java

Index: chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrProxyActivity.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrProxyActivity.java b/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrProxyActivity.java
new file mode 100644
index 0000000000000000000000000000000000000000..644c14d3ae5959952b406f41a2be4426c709cd07
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrProxyActivity.java
@@ -0,0 +1,60 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.chrome.browser.vr_shell;
+
+import android.app.Activity;
+import android.app.ActivityManager;
+import android.os.Bundle;
+import android.os.StrictMode;
+
+import org.chromium.base.Log;
+
+import java.io.BufferedReader;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.io.InputStreamReader;
+
+/**
+ * Dispatches incoming intents to the appropriate VR activity based on the VR intent extras.
+ */
+public class VrProxyActivity extends Activity {
+    private static final String TAG = "VrProxyActivity";
+
+    @Override
+    public void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        Log.v(TAG, "VR DON flow success, resuming Chrome in VR.");
+
+        ActivityManager activityManager = (ActivityManager) getSystemService(ACTIVITY_SERVICE);
+
+        // TODO(mthiesse): See VrShellDelegate#launchInVR
+        StrictMode.ThreadPolicy oldPolicy = StrictMode.allowThreadDiskReads();
+        StrictMode.allowThreadDiskWrites();
+        File dir = VrShellDelegate.getOrCreateVRDirectory();
+        File tidFile = new File(dir, VrShellDelegate.TID_FILE);

[Ted C, 2017/03/31 18:17:18]

Are we worried about Chrome dying while this is happening?  Any reason we don't
just use a static variable in this class and a public static setter?

[mthiesse, 2017/03/31 20:06:14]

Wouldn't we have to somehow start the VrProxyActivity in the process that the
CCT runs in so that they can read the same memory? I'm not sure how we would go
about doing that. I did try this at first, but I was reading default values from
VrProxyActivity instead of the values I set. If you expect this to work I can
take another look.

+        File resultFile = new File(dir, VrShellDelegate.RESULT_SUCCESS_FILE);

[Ted C, 2017/03/31 18:17:18]

same thing, are we not calling directly into our own activity as a result of
this?  why can't we use statics if we're in the same process?

+        try {

[Ted C, 2017/03/31 18:17:18]

you don't need nested try catches.

this can be:

try {
} catch (Exceptions) {
} finally {
}

+            try {
+                BufferedReader stream =
+                        new BufferedReader(new InputStreamReader(new FileInputStream(tidFile)));
+                String line = stream.readLine();
+                stream.close();
+                if (line == null) throw new IOException();
+                int tid = Integer.parseInt(line);
+                resultFile.createNewFile();
+                finish();
+                activityManager.moveTaskToFront(tid, 0);

[Ted C, 2017/03/31 18:17:18]

does this need to happen after finish?  I'm wondering if finish could go into
the finally block.

+            } catch (IOException | NumberFormatException e) {
+                Log.e(TAG, "Failed to read file: " + tidFile.getAbsolutePath());
+                finish();
+                return;
+            }
+        } finally {
+            tidFile.delete();
+            StrictMode.setThreadPolicy(oldPolicy);
+        }
+    }
+}