Support "display": "fullscreen" for sites added to the home screen.

chrome/android/java/src/org/chromium/chrome/browser/webapps/FullScreenActivity.java

Index: chrome/android/java/src/org/chromium/chrome/browser/webapps/FullScreenActivity.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/webapps/FullScreenActivity.java b/chrome/android/java/src/org/chromium/chrome/browser/webapps/FullScreenActivity.java
index 901b62b51f70f11bef575b192284684282548dd1..dc4f65203a0e269c0e2da5c0a5396d50971c0d44 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/webapps/FullScreenActivity.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/webapps/FullScreenActivity.java
@@ -5,8 +5,10 @@
 package org.chromium.chrome.browser.webapps;
 
 import android.content.Intent;
+import android.os.Build;
 import android.util.Pair;
 import android.view.View;
+import android.view.View.OnSystemUiVisibilityChangeListener;
 import android.view.ViewGroup;
 
 import org.chromium.base.annotations.SuppressFBWarnings;
@@ -46,6 +48,20 @@ public abstract class FullScreenActivity extends ChromeActivity {
     protected static final String BUNDLE_TAB_URL = "tabUrl";
     private static final String TAG = "FullScreenActivity";
 
+    private static final int ENTER_IMMERSIVE_MODE_DELAY_MILLIS = 300;

[Ted C, 2017/01/20 05:47:07]

any reason all of this logic isn't in WebappActivity?  Doesn't "seem" to be used
by this class at all.

[Leo, 2017/01/23 01:14:27]

Original changes was in WebappActivity. Somehow I found since its parent's name
is FullScreenActivity which doesn't support really full-screen mode. So maybe
it's better to implement the "full-screen" mode in the parent class, then all
the subclass could easily support "full-screen" mode.

[Ted C, 2017/01/23 19:01:08]

Fullscreen in the name of this activity means that it doesn't show an omnibox. 
So, full-screen mode here is very Webapp specific.

Also as a general rule, it is best to keep the code isolated to the class that
needs it and generalize it later.  It isn't hard to move in the future, but for
now it makes it harder to read being split between two classes.

[Leo, 2017/02/07 07:52:49]

Thanks for the advice. Moved all changes to WebappActivity.

+    private static final int RESTORE_IMMERSIVE_MODE_DELAY_MILLIS = 3000;
+    private static final int IMMERSIVE_MODE_UI_FLAGS =
+            View.SYSTEM_UI_FLAG_LAYOUT_STABLE
+                | View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
+                | View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
+                | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION // hide nav bar
+                | View.SYSTEM_UI_FLAG_FULLSCREEN // hide status bar
+                | View.SYSTEM_UI_FLAG_LOW_PROFILE
+                | View.SYSTEM_UI_FLAG_IMMERSIVE;
+
+    private boolean mEnteredImmersive;
+    private Runnable mSetImmersiveRunnable;
+
     private Tab mTab;
 
     private WebContents mWebContents;
@@ -179,6 +195,61 @@ public abstract class FullScreenActivity extends ChromeActivity {
         };
     }
 
+    @Override
+    public void onWindowFocusChanged(boolean hasFocus) {
+        super.onWindowFocusChanged(hasFocus);
+
+        if (hasFocus && (mSetImmersiveRunnable != null)) {

[Ted C, 2017/01/20 05:47:07]

the () around the null check aren't needed

[Leo, 2017/01/23 01:14:27]

Thanks for the catch. 

Use asyncSetImmersive here instead of enterImmersiveMode. So it no-ops before
mSetImmersiveRunnable was not initialized.

+            enterImmersiveMode(getWindow().getDecorView());

[Ted C, 2017/01/20 05:47:07]

looks like both call sites just pass in getWindow().getDecorView(), any reason
to not just do that internally in the method?

[Leo, 2017/01/23 01:14:27]

Sure, getWindow().getDecorView() can be used internally. My intent is try to
make sure the user understand that enterImmersiveMode should be called at a
proper time (after Decor View was ready).

I can remove the arg and add more comments instead. WDYT?

[Ted C, 2017/01/23 19:01:08]

I would just remove the variable.  getDecorView() will build the view lazily so
I think it would just confuse api consumers if you add documentation about decor
view lifetime.

[Leo, 2017/02/07 07:52:48]

Done.

+        }
+    }
+
+    /**
+     * Sets the given decor {@link View} into an immersive mode.
+     * If immersive mode is not supported, this method no-ops.
+     */
+    protected void enterImmersiveMode(final View decor) {
+        // Immersive mode is only supported in API 19+.
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.KITKAT) return;
+
+        if (mSetImmersiveRunnable == null) {
+            mSetImmersiveRunnable = new Runnable() {
+                @Override
+                public void run() {
+                    int currentFlags = decor.getSystemUiVisibility();
+                    int desiredFlags = currentFlags | IMMERSIVE_MODE_UI_FLAGS;
+                    if (currentFlags != desiredFlags) {
+                        decor.setSystemUiVisibility(desiredFlags);
+                    }
+                }
+            };
+        }
+
+        // When we enter immersive mode for the first time, register a
+        // SystemUiVisibilityChangeListener that restores immersive mode. This is necessary
+        // because user actions like focusing a keyboard will break out of immersive mode.
+        if (!mEnteredImmersive) {

[Ted C, 2017/01/20 05:47:07]

can we just put this block in the mSetImmersiveRunnable == null block above? 
Seems like we could use just one variable as a signal for initial pass (i.e.
delete mEnteredImmersive).

[Leo, 2017/01/23 01:14:27]

Thanks for the tips, Done.

+            decor.setOnSystemUiVisibilityChangeListener(new OnSystemUiVisibilityChangeListener() {
+                @Override
+                public void onSystemUiVisibilityChange(int newFlags) {
+                    if ((newFlags & View.SYSTEM_UI_FLAG_FULLSCREEN) == 0) {
+                        asyncSetImmersive(RESTORE_IMMERSIVE_MODE_DELAY_MILLIS);

[Ted C, 2017/01/20 05:47:07]

3 seconds seems like a very long time.  Why does it need to be that high?

[Leo, 2017/01/23 01:14:27]

In most scenarios, immersive mode will be restored after users triggers some
event to show system status bar or navigation bar. The delay here is used to
give user some time to make the next choice.

Here is a demo video for 3 seconds delay.
https://drive.google.com/a/chromium.org/file/d/0B7BQekACXW_VRGVkanQzS09ZN1U/v...

What's your suggestion for the delay setting?

[Ted C, 2017/01/23 19:01:08]

That video looks good to me.  Good to know the context.

[Leo, 2017/02/07 07:52:49]

Acknowledged.

+                    }
+                }
+            });
+        }
+
+        asyncSetImmersive(ENTER_IMMERSIVE_MODE_DELAY_MILLIS);
+        mEnteredImmersive = true;
+    }
+
+    private void asyncSetImmersive(int delayInMills) {
+        if (mSetImmersiveRunnable == null) return;
+
+        mHandler.removeCallbacks(mSetImmersiveRunnable);
+        mHandler.postDelayed(mSetImmersiveRunnable, delayInMills);
+    }
+
     /**
      * @return {@link TabDelegateFactory} to be used while creating the associated {@link Tab}.
      */