[Android] Add animation frame time histogram class.

base/android/java/src/org/chromium/base/AnimationFrameTimeHistogram.java

Index: base/android/java/src/org/chromium/base/AnimationFrameTimeHistogram.java
diff --git a/base/android/java/src/org/chromium/base/AnimationFrameTimeHistogram.java b/base/android/java/src/org/chromium/base/AnimationFrameTimeHistogram.java
new file mode 100644
index 0000000000000000000000000000000000000000..3f9060c19a9ca708c1f4a7929b9bf25756378017
--- /dev/null
+++ b/base/android/java/src/org/chromium/base/AnimationFrameTimeHistogram.java
@@ -0,0 +1,109 @@
+// 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.base;
+
+import android.util.Log;
+import android.view.Choreographer;
+import android.view.Choreographer.FrameCallback;
+
+/**
+ * Record Android animation frame rate and save it to UMA histogram. This is mainly for monitoring
+ * any jankiness of short Chrome Android animations. It is limited to few seconds of recording.
+ */
+public class AnimationFrameTimeHistogram {
+    private static final String TAG = "AnimationFrameTimeHistogram";
+    private static final int MAX_FRAME_TIME_NUM = 600; // 10 sec on 60 fps.
+
+    private final String mHistogramName;
+    private Recorder mRecorder;
+
+    /**
+     * @param histogramName The histogram name that the recorded frame times will be saved.
+     *                      This must be also defined in histograms.xml
+     */
+    public AnimationFrameTimeHistogram(String histogramName) {
+        mHistogramName = histogramName;
+    }
+
+    /**
+     * Start recording frame times. The recording can fail if it exceeds a few seconds.
+     */
+    public void startRecording() {
+        mRecorder = new Recorder();
+        mRecorder.startRecording();
+    }
+
+    /**
+     * End recording and save it to histogram. It won't save histogram if the recording wasn't
+     * successful.
+     */
+    public void endRecording() {
+        if (mRecorder.endRecording()) {
+            nativeSaveHistogram(mHistogramName,
+                    mRecorder.getFrameTimesNs(), mRecorder.getFrameTimesCount());
+        }
+        mRecorder = null;
+    }
+
+    /**
+     * Record Android animation frame rate and return the result.
+     */
+    private static class Recorder implements FrameCallback {
+        private final Choreographer mChoreographer = Choreographer.getInstance();
+        private final long[] mFrameTimesNs = new long[MAX_FRAME_TIME_NUM];
+        private boolean mIsRecording;
+        private long mPrevFrameTimeNs;
+        private int mFrameTimesCount;
+
+        private void startRecording() {
+            mIsRecording = true;
+            mFrameTimesCount = -1;
+            mChoreographer.postFrameCallback(this);
+        }
+
+        /**
+         * @return Whether the recording was successful. If successful, the result is available via
+         *         getFrameTimesNs and getFrameTimesCount.
+         */
+        private boolean endRecording() {
+            boolean succeeded = mIsRecording;
+            mIsRecording = false;
+            return succeeded;
+        }
+
+        private long[] getFrameTimesNs() {
+            return mFrameTimesNs;
+        }
+
+        private int getFrameTimesCount() {
+            return mFrameTimesCount;
+        }
+
+        @Override
+        public void doFrame(long frameTimeNs) {
+            if (!mIsRecording) {
+                return;
+            }
+
+            if (mFrameTimesCount == mFrameTimesNs.length) {
+                mIsRecording = false;
+                Log.w(TAG, "Animation frame time recording reached the maximum number. It's either"
+                        + "the animation took too long or recording end is not called.");
+                return;
+            }
+
+            long timeDiffNs = frameTimeNs - mPrevFrameTimeNs;
+            mPrevFrameTimeNs = frameTimeNs;
+            if (mFrameTimesCount > -1) {
+                mFrameTimesNs[mFrameTimesCount] = timeDiffNs;
+            }
+
+            ++mFrameTimesCount;
+            mChoreographer.postFrameCallback(this);
+        }
+    }
+
+    private native void nativeSaveHistogram(String histogramName, long[] frameTimesNs, int count);
+}