Fix compile error in Chromium OS.

isfinite is only defined in the std namespace in Chromium OS.

Bug: Note
TEST=emerge-link update_engine

Change-Id: I0f408f14f207d845d4fae06f61cc6929f25d0ad6
diff --git a/payload_consumer/postinstall_runner_action.cc b/payload_consumer/postinstall_runner_action.cc
index db1ec3c..bb9ffe4 100644
--- a/payload_consumer/postinstall_runner_action.cc
+++ b/payload_consumer/postinstall_runner_action.cc
@@ -23,6 +23,8 @@
 #include <sys/types.h>
 #include <unistd.h>
 
+#include <cmath>
+
 #include <base/files/file_path.h>
 #include <base/files/file_util.h>
 #include <base/logging.h>
@@ -240,7 +242,7 @@
     delegate_->ProgressUpdate(1.);
     return;
   }
-  if (!isfinite(frac) || frac < 0)
+  if (!std::isfinite(frac) || frac < 0)
     frac = 0;
   if (frac > 1)
     frac = 1;