[Cronet] Change sample app to save netlog to app's files directory

components/cronet/android/sample/src/org/chromium/cronet_sample_apk/CronetSampleActivity.java

Index: components/cronet/android/sample/src/org/chromium/cronet_sample_apk/CronetSampleActivity.java
diff --git a/components/cronet/android/sample/src/org/chromium/cronet_sample_apk/CronetSampleActivity.java b/components/cronet/android/sample/src/org/chromium/cronet_sample_apk/CronetSampleActivity.java
index 52cfc9bdab6b05e82d51917624ccf49b9cc251c4..02bbc9cb2a0b36be67427e03c62e0f6a9e753755 100644
--- a/components/cronet/android/sample/src/org/chromium/cronet_sample_apk/CronetSampleActivity.java
+++ b/components/cronet/android/sample/src/org/chromium/cronet_sample_apk/CronetSampleActivity.java
@@ -8,7 +8,6 @@ import android.app.Activity;
 import android.app.AlertDialog;
 import android.content.DialogInterface;
 import android.os.Bundle;
-import android.os.Environment;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.widget.EditText;
@@ -175,12 +174,16 @@ public class CronetSampleActivity extends Activity {
         builder.build().start();
     }
 
+    // Starts writing NetLog to disk. startNetLog() should be called afterwards.
     private void startNetLog() {
-        mCronetEngine.startNetLogToFile(
-                Environment.getExternalStorageDirectory().getPath() + "/cronet_sample_netlog.json",
-                false);
+        mCronetEngine.startNetLogToFile(getCacheDir().getPath() + "/netlog.json", false);
     }
 
+    // Stops writing NetLog to disk. Should be called after calling startNetLog().
+    // NetLog can be downloaded afterwards via:
+    //   adb root
+    //   adb pull /data/data/org.chromium.cronet_sample_apk/cache/netlog.json
+    // netlog.json can then be viewed in a Chrome tab navigated to chrome://net-internals/#import
     private void stopNetLog() {
         mCronetEngine.stopNetLog();
     }