Rename TARGET_OS_* to HOST_OS_*.

runtime/vm/timeline.cc

Index: runtime/vm/timeline.cc
diff --git a/runtime/vm/timeline.cc b/runtime/vm/timeline.cc
index 4c23d78c8a14d44cb15e27bd5fde5c89a0929022..716ac8b7b098f1f382fe3be1c0b5d1f7772d76c4 100644
--- a/runtime/vm/timeline.cc
+++ b/runtime/vm/timeline.cc
@@ -1375,7 +1375,7 @@ void TimelineEventFixedBufferRecorder::CompleteEvent(TimelineEvent* event) {
 
 TimelineEventSystraceRecorder::TimelineEventSystraceRecorder(intptr_t capacity)
     : TimelineEventFixedBufferRecorder(capacity), systrace_fd_(-1) {
-#if defined(TARGET_OS_ANDROID) || defined(TARGET_OS_LINUX)
+#if defined(HOST_OS_ANDROID) || defined(HOST_OS_LINUX)
   const char* kSystracePath = "/sys/kernel/debug/tracing/trace_marker";
   systrace_fd_ = open(kSystracePath, O_WRONLY);
   if ((systrace_fd_ < 0) && FLAG_trace_timeline) {
@@ -1391,7 +1391,7 @@ TimelineEventSystraceRecorder::TimelineEventSystraceRecorder(intptr_t capacity)
 
 
 TimelineEventSystraceRecorder::~TimelineEventSystraceRecorder() {
-#if defined(TARGET_OS_ANDROID) || defined(TARGET_OS_LINUX)
+#if defined(HOST_OS_ANDROID) || defined(HOST_OS_LINUX)
   if (systrace_fd_ >= 0) {
     close(systrace_fd_);
   }
@@ -1416,7 +1416,7 @@ void TimelineEventSystraceRecorder::CompleteEvent(TimelineEvent* event) {
   if (event == NULL) {
     return;
   }
-#if defined(TARGET_OS_ANDROID) || defined(TARGET_OS_LINUX)
+#if defined(HOST_OS_ANDROID) || defined(HOST_OS_LINUX)
   if (systrace_fd_ >= 0) {
     // Serialize to the systrace format.
     const intptr_t kBufferLength = 1024;