Create open source LeakCanary plugin

Summary: Adds a new plugin to support [LeakCanary](https://github.com/square/leakcanary), displaying memory leaks as they are detected. Each leak shows a hierarchical path from the GC root to the leaked object, and allows inspection of these objects' fields.

Reviewed By: jknoxville

Differential Revision: D8865149

fbshipit-source-id: 99bcf216578b9d6660ead7d48b9bafe0d20a6c08

docs/leak-canary-plugin.md

@@ -0,0 +1,33 @@
+---
+id: leak-canary-plugin
+title: LeakCanary
+---
+
+The LeakCanary plugin provides developers with Sonar support for [LeakCanary](https://github.com/square/leakcanary), an open source memory leak detection library.
+
+## Setup
+
+Note: this plugin is only available for Android.
+
+### Android
+
+First, add the plugin to your Sonar client instance:
+```java
+import com.facebook.sonar.plugins.leakcanary.LeakCanarySonarPlugin;
+
+client.addPlugin(new LeakCanarySonarPlugin());
+```
+
+Next, build a custom RefWatcher using RecordLeakService: (see [LeakCanary docs](https://github.com/square/leakcanary/wiki/Customizing-LeakCanary#uploading-to-a-server) for more information on RefWatcher)
+```java
+import com.facebook.sonar.plugins.leakcanary.RecordLeakService;
+
+RefWatcher refWatcher = LeakCanary.refWatcher(this)
+    .listenerServiceClass(RecordLeakService.class);
+    .buildAndInstall();
+```
+
+## Usage
+
+Leaks detected by LeakCanary will appear automatically in Sonar. Each leak will display a hierarchy of objects, beginning from the garbage collector root and ending at the leaked class.
+Selecting any object in this list will display contents of the object's various fields.