Turn the utility process image decoder into a Mojo service.

chrome/utility/chrome_content_utility_client.h

Index: chrome/utility/chrome_content_utility_client.h
diff --git a/chrome/utility/chrome_content_utility_client.h b/chrome/utility/chrome_content_utility_client.h
index 1d244197b55103bf0a95ed9f1dfd4691b7232d0d..18fe6b01e768baa5fa6c5e7e90044f0903941f8c 100644
--- a/chrome/utility/chrome_content_utility_client.h
+++ b/chrome/utility/chrome_content_utility_client.h
@@ -42,6 +42,14 @@ class ChromeContentUtilityClient : public content::ContentUtilityClient {
     max_ipc_message_size_ = max_message_size;
   }
 
+  // Reference counting for Mojo services. A reference count is incremented when
+  // Mojo services are connected to, and decremented when the connection is
+  // destroyed. When the count reaches 0, this process is freed. The assumption
+  // is that multiple Mojo services can be connected to in the same utility
+  // process. This is a Mojo alternative to "batch mode" for Chrome IPC.
+  void MojoRef();
+  void MojoUnref();
+
  private:
   // IPC message handlers.
   void OnUnpackWebResource(const std::string& resource_data);
@@ -84,6 +92,8 @@ class ChromeContentUtilityClient : public content::ContentUtilityClient {
   // Maximum IPC msg size (default to kMaximumMessageSize; override for testing)
   static int64_t max_ipc_message_size_;
 
+  int32_t mojo_service_ref_count_;
+
   DISALLOW_COPY_AND_ASSIGN(ChromeContentUtilityClient);
 };