[Cronet] Adjust to Android M permissions model

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..b28f0af25748755a2fb7879a847fc712f8b8bd43 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
@@ -4,15 +4,20 @@
 
 package org.chromium.cronet_sample_apk;
 
+import android.Manifest;
 import android.app.Activity;
 import android.app.AlertDialog;
 import android.content.DialogInterface;
+import android.content.pm.PackageManager;
 import android.os.Bundle;
 import android.os.Environment;
+import android.support.v4.app.ActivityCompat;
+import android.support.v4.content.ContextCompat;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.widget.EditText;
 import android.widget.TextView;
+import android.widget.Toast;
 
 import org.chromium.base.Log;
 import org.chromium.net.CronetEngine;
@@ -35,6 +40,9 @@ import java.util.concurrent.Executors;
 public class CronetSampleActivity extends Activity {
     private static final String TAG = "CronetSample";
 
+    // Permisson request code used for requesting WRITE_EXTERNAL_STORAGE permisson.
+    private static final int MY_PERMISSIONS_REQUEST_WRITE_EXTERNAL_STORAGE = 1;
+
     private CronetEngine mCronetEngine;
 
     private String mUrl;
@@ -175,7 +183,51 @@ public class CronetSampleActivity extends Activity {
         builder.build().start();
     }
 
+    // Call this function to start writing NetLog to a file.
     private void startNetLog() {
+        // Follow the prescribed formula to get WRITE_EXTERNAL_STORAGE permission as per
+        // http://developer.android.com/training/permissions/requesting.html#perm-request
+        if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
+                == PackageManager.PERMISSION_GRANTED) {
+            // Permission granted already, start netlog diretly.
+            startNetLogWithPermission();
+        } else {
+            if (ActivityCompat.shouldShowRequestPermissionRationale(
+                        this, Manifest.permission.WRITE_EXTERNAL_STORAGE)) {
+                // User has denied permission; don't re-request but instead surface explanation.
+                Toast.makeText(this, "Storage access needed to write netlog.", Toast.LENGTH_SHORT)
+                        .show();
+            } else {
+                ActivityCompat.requestPermissions(this,
+                        new String[] {Manifest.permission.WRITE_EXTERNAL_STORAGE},
+                        MY_PERMISSIONS_REQUEST_WRITE_EXTERNAL_STORAGE);
+            }
+        }
+    }
+
+    @Override
+    public void onRequestPermissionsResult(
+            int requestCode, String permissions[], int[] grantResults) {
+        switch (requestCode) {
+            case MY_PERMISSIONS_REQUEST_WRITE_EXTERNAL_STORAGE: {
+                if (grantResults.length > 0
+                        && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
+                    // Permission granted, start netlog.
+                    startNetLogWithPermission();
+                } else {
+                    // Permission denied, surface corresponding error message.
+                    Toast.makeText(this, "Netlog cannot be written without storage access.",
+                                 Toast.LENGTH_SHORT)
+                            .show();
+                }
+                return;
+            }
+        }
+    }
+
+    // Starts writing NetLog to file.  Call startNetLog() unless WRITE_EXTERNAL_STORAGE permission
+    // is known to have been granted.
+    private void startNetLogWithPermission() {
         mCronetEngine.startNetLogToFile(
                 Environment.getExternalStorageDirectory().getPath() + "/cronet_sample_netlog.json",
                 false);