Fix missing symbols for pre-linking of the Cast sender library for iOS.

base/process/process_metrics_ios.cc

Index: base/process/process_metrics_ios.cc
diff --git a/base/process/process_metrics_ios.cc b/base/process/process_metrics_ios.cc
index 9ae838d39a0b4ec341c36a52a32accd7a78c7ec1..c00d51158ddac0884866ea24b744a4e223c57094 100644
--- a/base/process/process_metrics_ios.cc
+++ b/base/process/process_metrics_ios.cc
@@ -30,6 +30,10 @@ ProcessMetrics* ProcessMetrics::CreateProcessMetrics(ProcessHandle process) {
   return new ProcessMetrics(process);
 }
 
+double ProcessMetrics::GetCPUUsage() {
+  return 0;
+}
+
 size_t ProcessMetrics::GetPagefileUsage() const {
   task_basic_info_64 task_info_data;
   if (!GetTaskInfo(&task_info_data))
@@ -69,4 +73,9 @@ size_t GetPageSize() {
   return getpagesize();
 }
 
+// Bytes committed by the system.
+size_t GetSystemCommitCharge() {
+  return 0;
+}
+
 }  // namespace base