Replace some platform macros with USE_ZYGOTE_HANDLE

Wrap the definition of member named is_broker_ in
PpapiPluginSandboxedProcessLauncherDelegate class with
USE_ZYGOTE_HANDLE || OS_WIN, since it is used only from code blocks
enclosed by either of those conditions.

The existing conditions were probably a leftover from before
USE_ZYGOTE_HANDLE was introduced.

Related: https://chromium-review.googlesource.com/862298
Change-Id: I4a2814ace7f2b4280c0c1d69082e78fd626187ed
Reviewed-on: https://chromium-review.googlesource.com/1019246Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#553574}

content/browser/ppapi_plugin_process_host.cc

@@ -58,8 +58,7 @@ class PpapiPluginSandboxedProcessLauncherDelegate
     : public content::SandboxedProcessLauncherDelegate {
  public:
   explicit PpapiPluginSandboxedProcessLauncherDelegate(bool is_broker)
-#if (defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_ANDROID)) || \
-    defined(OS_WIN)
+#if BUILDFLAG(USE_ZYGOTE_HANDLE) || defined(OS_WIN)
       : is_broker_(is_broker)
 #endif
   {
@@ -124,8 +123,7 @@ class PpapiPluginSandboxedProcessLauncherDelegate
   }
 
  private:
-#if (defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_ANDROID)) || \
-    defined(OS_WIN)
+#if BUILDFLAG(USE_ZYGOTE_HANDLE) || defined(OS_WIN)
   bool is_broker_;
 #endif