Add systrace logging to ScopedCodeCacheWrite

Shows if we are taking a long time to mprotect.

Bug: 27502458

(cherry picked from commit 462cd2cfa8c5fbb6548419eb8f27b448a12aca11)

Change-Id: Ic0f24641f5856b13f3b949dcd53dc01ec952d171
diff --git a/runtime/jit/jit_code_cache.cc b/runtime/jit/jit_code_cache.cc
index 1545cb7..0b0f926 100644
--- a/runtime/jit/jit_code_cache.cc
+++ b/runtime/jit/jit_code_cache.cc
@@ -169,12 +169,16 @@
   return false;
 }
 
-class ScopedCodeCacheWrite {
+class ScopedCodeCacheWrite : ScopedTrace {
  public:
-  explicit ScopedCodeCacheWrite(MemMap* code_map) : code_map_(code_map) {
+  explicit ScopedCodeCacheWrite(MemMap* code_map)
+      : ScopedTrace("ScopedCodeCacheWrite"),
+        code_map_(code_map) {
+    ScopedTrace trace("mprotect all");
     CHECKED_MPROTECT(code_map_->Begin(), code_map_->Size(), kProtAll);
   }
   ~ScopedCodeCacheWrite() {
+    ScopedTrace trace("mprotect code");
     CHECKED_MPROTECT(code_map_->Begin(), code_map_->Size(), kProtCode);
   }
  private: