Return $this from setters

Summary:
Most setters returns `$this` but some don't.
I guess it's not by purpose.

Test Plan:
  arc lint

Reviewers: epriestley

Reviewed By: epriestley

CC: aran

Differential Revision: https://secure.phabricator.com/D2084

src/branch/BranchInfo.php

@@ -77,6 +77,7 @@ final class BranchInfo {
 
   public function setCurrent() {
     $this->currentHead = true;
+    return $this;
   }
 
   public function isCurrentHead() {
@@ -86,6 +87,7 @@ final class BranchInfo {
 
   public function setStatus($status) {
     $this->status = $status;
+    return $this;
   }
 
   public function getStatus() {

src/lint/engine/base/ArcanistLintEngine.php

@@ -119,6 +119,7 @@ abstract class ArcanistLintEngine {
 
   public function setHookAPI(ArcanistHookAPI $hook_api) {
     $this->hookAPI  = $hook_api;
+    return $this;
   }
 
   public function getHookAPI() {

src/lint/linter/phutilmodule/ArcanistPhutilModuleLinter.php

@@ -73,6 +73,7 @@ final class ArcanistPhutilModuleLinter extends ArcanistLinter {
 
   private function setModuleInfo($key, array $info) {
     $this->moduleInfo[$key] = $info;
+    return $this;
   }
 
   private function getModulePathOnDisk($key) {

src/parser/bundle/ArcanistBundle.php

@@ -34,10 +34,12 @@ final class ArcanistBundle {
 
   public function setConduit(ConduitClient $conduit) {
     $this->conduit = $conduit;
+    return $this;
   }
 
   public function setProjectID($project_id) {
     $this->projectID = $project_id;
+    return $this;
   }
 
   public function getProjectID() {
@@ -46,6 +48,7 @@ final class ArcanistBundle {
 
   public function setBaseRevision($base_revision) {
     $this->baseRevision = $base_revision;
+    return $this;
   }
 
   public function setEncoding($encoding) {

src/parser/diff/ArcanistDiffParser.php

@@ -50,6 +50,7 @@ final class ArcanistDiffParser {
 
   public function setTryEncoding($encoding) {
     $this->tryEncoding = $encoding;
+    return $this;
   }
 
   public function forcePath($path) {

src/unit/engine/base/ArcanistBaseUnitTestEngine.php

@@ -65,6 +65,7 @@ abstract class ArcanistBaseUnitTestEngine {
 
   final public function setEnableAsyncTests($enable_async_tests) {
     $this->enableAsyncTests = $enable_async_tests;
+    return $this;
   }
 
   final public function getEnableAsyncTests() {
@@ -89,6 +90,7 @@ abstract class ArcanistBaseUnitTestEngine {
    */
   public function setDifferentialDiffID($id) {
     $this->diffID = $id;
+    return $this;
   }
 
   /**

src/workflow/unit/ArcanistUnitWorkflow.php

@@ -269,6 +269,7 @@ EOTEXT
     if ($this->engine) {
       $this->engine->setDifferentialDiffID($id);
     }
+    return $this;
   }
 
   private static function formatTestDuration($seconds) {