[Android] Add animation frame time histogram class.

base/android/animation_frame_time_histogram.cc

+// 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.
+
+#include "base/android/animation_frame_time_histogram.h"
+
+#include "base/android/jni_string.h"
+#include "base/metrics/histogram_macros.h"
+#include "jni/AnimationFrameTimeHistogram_jni.h"
+
+// static
+void SaveHistogram(JNIEnv* env,
+                   jobject jcaller,
+                   jstring j_histogram_name,
+                   jlongArray j_frame_times_ms,
+                   jint j_count) {
+  jlong *frame_times_ns = env->GetLongArrayElements(j_frame_times_ms, NULL);
+  std::string histogram_name = base::android::ConvertJavaStringToUTF8(
+      env, j_histogram_name);
+
+  for (int i = 0; i < j_count; ++i) {

[nyquist, 2015/02/27 04:02:19]

size_t?

[Kibeom Kim (inactive), 2015/02/27 19:56:40]

Currently j_count is jint type so I'm getting "comparison between signed and
unsigned integer expressions [-Werror=sign-compare]" for using size_t here. Do
you think it's better to change j_count to unsigned also?

+    UMA_HISTOGRAM_TIMES(histogram_name.c_str(),
+                        base::TimeDelta::FromMilliseconds(frame_times_ns[i]));
+  }
+}
+
+namespace base {
+namespace android {
+
+// static
+bool RegisterAnimationFrameTimeHistogram(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+}  // namespace android
+}  // namespace base