Import jsr305 and use it to mark @Nullable stuff.

This library is a provided dependency and is not necessary to be included
by OkHttp users.

This currently covers the okhttp and okhttp-logging-interceptor modules
only. It does not cover the 'internal' package in OkHttp, or its test cases.
We can add those as needed.

okhttp-logging-interceptor/pom.xml

@@ -18,6 +18,11 @@
       <artifactId>okhttp</artifactId>
       <version>${project.version}</version>
     </dependency>
+    <dependency>
+      <groupId>com.google.code.findbugs</groupId>
+      <artifactId>jsr305</artifactId>
+      <scope>provided</scope>
+    </dependency>
 
     <dependency>
       <groupId>junit</groupId>

okhttp-logging-interceptor/src/main/java/okhttp3/logging/package-info.java

@@ -0,0 +1,3 @@
+/** An OkHttp interceptor which logs HTTP request and response data. */
+@javax.annotation.ParametersAreNonnullByDefault
+package okhttp3.logging;