[Andorid] ClipDrawable progress bar experiment.

chrome/android/java/src/org/chromium/chrome/browser/widget/ClipDrawableProgressBar.java

+// Copyright 2015 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.widget;
+
+import android.content.Context;
+import android.util.AttributeSet;
+import android.widget.ImageView;
+
+/**
+ * An alternative progress bar implemented using ClipDrawable. We're experimenting with this for
+ * faster performance. http://crbug.com/455891
+ */
+public class ClipDrawableProgressBar extends ImageView {
+    private static final long PROGRESS_CLEARING_DELAY_MS = 200;
+
+    private final Runnable mClearLoadProgressRunnable = new Runnable() {
+        @Override
+        public void run() {
+            setProgress(0);
+        }
+    };
+
+    /**
+     * Constructor for inflating from XML.
+     */
+    public ClipDrawableProgressBar(Context context, AttributeSet attrs) {
+        super(context, attrs);
+    }
+
+    /**
+     * Set the current progress to the specified value.
+     * @param progress The new progress, between 0 and 10000.
+     */
+    public void setProgress(int progress) {
+        getDrawable().setLevel(progress);
+
+        removeCallbacks(mClearLoadProgressRunnable);
+        if (progress == 10000) postDelayed(mClearLoadProgressRunnable, PROGRESS_CLEARING_DELAY_MS);
+    }
+
+    /**
+     * Get the progress bar's current level of progress.
+     * @return The current progress, between 0 and getMax().
+     */
+    public int getProgress() {
+        return getDrawable().getLevel();
+    }
+}