Make JSONParser a pure interface.

components/safe_json/safe_json_parser.cc

Index: components/safe_json/safe_json_parser.cc
diff --git a/components/safe_json/safe_json_parser.cc b/components/safe_json/safe_json_parser.cc
index af30a19f2d7be77f18052233b91acff618c1e833..4d76c6f81b35554f17ab884023d08fe642e87466 100644
--- a/components/safe_json/safe_json_parser.cc
+++ b/components/safe_json/safe_json_parser.cc
@@ -6,7 +6,7 @@
 
 #include <string>
 
-#include "base/single_thread_task_runner.h"
+#include "base/sequenced_task_runner.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/thread_task_runner_handle.h"
 #include "base/tuple.h"
@@ -14,6 +14,7 @@
 #include "components/safe_json/safe_json_parser_messages.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/utility_process_host.h"
+#include "content/public/browser/utility_process_host_client.h"
 #include "grit/components_strings.h"
 #include "ipc/ipc_message_macros.h"
 #include "ui/base/l10n/l10n_util.h"
@@ -23,26 +24,69 @@ using content::UtilityProcessHost;
 
 namespace safe_json {
 
-SafeJsonParser::SafeJsonParser(const std::string& unsafe_json,
-                               const SuccessCallback& success_callback,
-                               const ErrorCallback& error_callback)
+namespace {
+
+SafeJsonParser::Factory g_factory = nullptr;
+
+class SafeJsonParserImpl : public content::UtilityProcessHostClient,
+                           public SafeJsonParser {
+ public:
+  SafeJsonParserImpl(const std::string& unsafe_json,
+                     const SuccessCallback& success_callback,
+                     const ErrorCallback& error_callback);
+
+  void Start() override;
+
+ private:
+  ~SafeJsonParserImpl() override;
+
+  void StartWorkOnIOThread();
+
+  void OnJSONParseSucceeded(const base::ListValue& wrapper);
+  void OnJSONParseFailed(const std::string& error_message);
+
+  void ReportResults();
+  void ReportResultsOnOriginThread();
+
+  // Implementing pieces of the UtilityProcessHostClient interface.
+  bool OnMessageReceived(const IPC::Message& message) override;
+
+  const std::string unsafe_json_;
+  SuccessCallback success_callback_;
+  ErrorCallback error_callback_;
+  scoped_refptr<base::SequencedTaskRunner> caller_task_runner_;
+
+  scoped_ptr<base::Value> parsed_json_;
+  std::string error_;
+
+  DISALLOW_COPY_AND_ASSIGN(SafeJsonParserImpl);
+};
+
+SafeJsonParserImpl::SafeJsonParserImpl(const std::string& unsafe_json,
+                                       const SuccessCallback& success_callback,
+                                       const ErrorCallback& error_callback)
     : unsafe_json_(unsafe_json),
       success_callback_(success_callback),
-      error_callback_(error_callback) {
-}
+      error_callback_(error_callback) {}
+
+void SafeJsonParserImpl::Start() {
+  // Current callers of this class are known to either come from
+  // the UI or IO threads. This DCHECK can be removed/further enhanced
+  // in case this class is useable outside of these contexts.
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI) ||
+         BrowserThread::CurrentlyOn(BrowserThread::IO));
 
-void SafeJsonParser::Start() {
   caller_task_runner_ = base::ThreadTaskRunnerHandle::Get();
 
   BrowserThread::PostTask(
       BrowserThread::IO, FROM_HERE,
-      base::Bind(&SafeJsonParser::StartWorkOnIOThread, this));
+      base::Bind(&SafeJsonParserImpl::StartWorkOnIOThread, this));
 }
 
-SafeJsonParser::~SafeJsonParser() {
+SafeJsonParserImpl::~SafeJsonParserImpl() {
 }
 
-void SafeJsonParser::StartWorkOnIOThread() {
+void SafeJsonParserImpl::StartWorkOnIOThread() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
   UtilityProcessHost* host = UtilityProcessHost::Create(
       this, base::ThreadTaskRunnerHandle::Get().get());
@@ -51,7 +95,7 @@ void SafeJsonParser::StartWorkOnIOThread() {
   host->Send(new SafeJsonParserMsg_ParseJSON(unsafe_json_));
 }
 
-void SafeJsonParser::OnJSONParseSucceeded(const base::ListValue& wrapper) {
+void SafeJsonParserImpl::OnJSONParseSucceeded(const base::ListValue& wrapper) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
   const base::Value* value = NULL;
   CHECK(wrapper.Get(0, &value));
@@ -60,26 +104,22 @@ void SafeJsonParser::OnJSONParseSucceeded(const base::ListValue& wrapper) {
   ReportResults();
 }
 
-void SafeJsonParser::OnJSONParseFailed(const std::string& error_message) {
+void SafeJsonParserImpl::OnJSONParseFailed(const std::string& error_message) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
   error_ = error_message;
   ReportResults();
 }
 
-void SafeJsonParser::ReportResults() {
+void SafeJsonParserImpl::ReportResults() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
 
   caller_task_runner_->PostTask(
       FROM_HERE,
-      base::Bind(&SafeJsonParser::ReportResultsOnOriginThread, this));
+      base::Bind(&SafeJsonParserImpl::ReportResultsOnOriginThread, this));
 }
 
-void SafeJsonParser::ReportResultsOnOriginThread() {
-  // Current callers of this class are known to either come from
-  // the UI or IO threads. This DCHECK can be removed/further enhanced
-  // in case this class is useable outside of these contexts.
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI) ||
-         BrowserThread::CurrentlyOn(BrowserThread::IO));
+void SafeJsonParserImpl::ReportResultsOnOriginThread() {
+  DCHECK(caller_task_runner_->RunsTasksOnCurrentThread());
   if (error_.empty() && parsed_json_) {
     if (!success_callback_.is_null())
       success_callback_.Run(parsed_json_.Pass());
@@ -89,9 +129,9 @@ void SafeJsonParser::ReportResultsOnOriginThread() {
   }
 }
 
-bool SafeJsonParser::OnMessageReceived(const IPC::Message& message) {
+bool SafeJsonParserImpl::OnMessageReceived(const IPC::Message& message) {
   bool handled = true;
-  IPC_BEGIN_MESSAGE_MAP(SafeJsonParser, message)
+  IPC_BEGIN_MESSAGE_MAP(SafeJsonParserImpl, message)
     IPC_MESSAGE_HANDLER(SafeJsonParserHostMsg_ParseJSON_Succeeded,
                         OnJSONParseSucceeded)
     IPC_MESSAGE_HANDLER(SafeJsonParserHostMsg_ParseJSON_Failed,
@@ -101,4 +141,22 @@ bool SafeJsonParser::OnMessageReceived(const IPC::Message& message) {
   return handled;
 }
 
+}  // namespace
+
+// static
+void SafeJsonParser::SetFactoryForTesting(Factory factory) {
+  g_factory = factory;
+}
+
+// static
+SafeJsonParser* SafeJsonParser::Create(
+    const std::string& unsafe_json,
+    const SuccessCallback& success_callback,
+    const ErrorCallback& error_callback) {
+  if (g_factory)
+    return g_factory(unsafe_json, success_callback, error_callback);
+
+  return new SafeJsonParserImpl(unsafe_json, success_callback, error_callback);
+}
+
 }  // namespace safe_json