Add a file observer to monitor if there is a crash

chrome/android/java/src/org/chromium/chrome/browser/crash/MinidumpDirectoryObserver.java

+// Copyright 2016 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.crash;
+
+import android.content.Context;
+import android.content.Intent;
+import android.os.FileObserver;
+
+import org.chromium.base.ApplicationStatus;
+import org.chromium.base.Log;
+import org.chromium.base.ThreadUtils;
+import org.chromium.base.metrics.RecordUserAction;
+
+import java.io.File;
+
+/**
+ * This class is a singleton that holds utilities for observer to monitor the minidump directory.
+ */
+public final class MinidumpDirectoryObserver extends FileObserver {
+
+    private static final String TAG = "MinidumpDirObserver";
+
+    private static MinidumpDirectoryObserver sMinidumpDirectoryObserver;
+    private static Context sContext = ApplicationStatus.getApplicationContext();
+
+    public static final String MINIDUMP_EXPERIMENT_NAME = "AddMinidumpDirObserver";
+
+    public static void startObserverWatching() {
+        ThreadUtils.assertOnUiThread();
+        if (sMinidumpDirectoryObserver == null) {
+            sMinidumpDirectoryObserver = new MinidumpDirectoryObserver();
+        }
+        sMinidumpDirectoryObserver.startWatching();
+    }
+
+    private MinidumpDirectoryObserver() {
+        // The file observer detects MOVED_TO for renderer crash and GPU crash;

[no sievers, 2016/01/29 23:52:34]

nit: I'd just say 'child processes'. There's also the utility process and making
assumptions about the specific types is basically what your patch is fixing :)

[Menglin, 2016/01/30 00:29:11]

Done.

+        // it detects CREATE for browser crash
+        super(new File(sContext.getCacheDir(), CrashFileManager.CRASH_DUMP_DIR).toString(),
+                FileObserver.MOVED_TO);
+    }
+
+    /**
+     *  When a miniudump is detected, upload it to Google crash server
+     */
+    @Override
+    public void onEvent(int event, String path) {

[no sievers, 2016/01/29 23:52:34]

nit: Can you put a comment that this is happening on an off-thread so that
nobody adds some code here that's not thread-safe?

[Menglin, 2016/01/30 00:29:11]

Done.

+        if (CrashFileManager.isMinidumpMIMEFirstTry(path)) {
+            Intent intent = MinidumpUploadService.createFindAndUploadLastCrashIntent(sContext);
+            sContext.startService(intent);
+            Log.i(TAG, "Detects a new minidump %s sending intent to MinidumpUploadService", path);
+            RecordUserAction.record("MobileBreakpadUploadAttempt");

[no sievers, 2016/01/29 23:52:34]

This stat is still a bit broken, since the name suggests that we'd want to bump
it with every try.
But then recording UMA here requires native which means this code shouldn't be
in the upload service (since it would crash on intent redelivery where native is
not loaded).

[Menglin, 2016/01/30 00:29:12]

I will leave it as it is for now and fix that in a separate cl. Thanks

+        }
+    }
+}