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..81ad6d55d2c0b05429f62a5a593df61d4125eaa2 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;
+    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 mEnableImmersive;
+    private boolean mEnteredImmersive;
+
     private Tab mTab;
 
     private WebContents mWebContents;
@@ -179,6 +195,50 @@ public abstract class FullScreenActivity extends ChromeActivity {
         };
     }
 
+    @Override
+    public void onWindowFocusChanged(boolean hasFocus) {
+        super.onWindowFocusChanged(hasFocus);
+
+        if (hasFocus && mEnableImmersive) {
+            enterImmersiveMode(getWindow().getDecorView());
+        }
+    }
+
+    /**
+     * Ensure the given {@link View} is in fullscreen immersion if this device supports.
+     */
+    protected void enterImmersiveMode(final View decor) {
+        if (!supportsImmersiveMode()) {
+            return;
+        }
+        mEnableImmersive = true;
+
+        // Register a SystemUiVisibilityChangeListener to restore immersive mode.

[dominickn, 2017/01/16 22:49:01]

Can these comments be a little more descriptive? Something like:

// 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.

+        if (!mEnteredImmersive) {
+            decor.setOnSystemUiVisibilityChangeListener(new OnSystemUiVisibilityChangeListener() {
+                @Override
+                public void onSystemUiVisibilityChange(int newFlags) {
+                    delaySetImmersive(decor, newFlags, RESTORE_IMMERSIVE_MODE_DELAY_MILLIS);
+                }
+            });
+        }
+        // Set Immersive mode on demand.

[dominickn, 2017/01/16 22:49:01]

Nit: add a newline above this comment, and explain why you have a short delay to
enter

[Leo, 2017/01/18 05:09:40]

Actually I just follow the sample codes created by Google and copy the 300 ms as
a friendly delay.
IMO, the main purpose is just to be asynchronous. Setting a short delay is not
required but could tolerate some annoying system faults. 

https://android.googlesource.com/platform/development/+/e7a6ab4/samples/devby...

[dominickn, 2017/01/18 05:56:17]

Ah, I see, that makes sense.

+        delaySetImmersive(decor, decor.getSystemUiVisibility(), ENTER_IMMERSIVE_MODE_DELAY_MILLIS);
+        mEnteredImmersive = true;
+    }
+
+    private void delaySetImmersive(final View decor, final int flags, int delayInMills) {
+        mHandler.postDelayed(new Runnable() {
+            @Override
+            public void run() {
+                int desiredFlags = flags | IMMERSIVE_MODE_UI_FLAGS;
+                if (flags != desiredFlags) {
+                    decor.setSystemUiVisibility(desiredFlags);
+                }
+            }
+        }, delayInMills);
+    }
+
     /**
      * @return {@link TabDelegateFactory} to be used while creating the associated {@link Tab}.
      */
@@ -206,4 +266,11 @@ public abstract class FullScreenActivity extends ChromeActivity {
     @Override
     public void onCheckForUpdate(boolean updateAvailable) {
     }
+
+    /**
+     ** @return true if this device supports immersive mode functionality.
+     **/
+    public static boolean supportsImmersiveMode() {
+        return Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT;
+    }
 }