liblog: don't use a cache for __android_log_is_debuggable()

ro.debuggable is set by init before other processes would possibly
call __android_log_is_debuggable(), so this property can be checked
once and stored without liblog's property caching mechanisms.

Test: this function returns accurately
Change-Id: Idb1e5e10e53ca809b7f9a75164a4982f39827d4e
diff --git a/liblog/include/log/log_properties.h b/liblog/include/log/log_properties.h
index 3497d63..2a0230f 100644
--- a/liblog/include/log/log_properties.h
+++ b/liblog/include/log/log_properties.h
@@ -20,6 +20,7 @@
 extern "C" {
 #endif
 
+/* Returns `1` if the device is debuggable or `0` if not. */
 int __android_log_is_debuggable();
 
 #ifdef __cplusplus
diff --git a/liblog/properties.cpp b/liblog/properties.cpp
index 2a30a0b..9990137 100644
--- a/liblog/properties.cpp
+++ b/liblog/properties.cpp
@@ -294,33 +294,12 @@
 }
 
 int __android_log_is_debuggable() {
-  static uint32_t serial;
-  static struct cache_char tag_cache;
-  static const char key[] = "ro.debuggable";
-  int ret;
+  static int is_debuggable = [] {
+    char value[PROP_VALUE_MAX] = {};
+    return __system_property_get("ro.debuggable", value) > 0 && !strcmp(value, "1");
+  }();
 
-  if (tag_cache.c) { /* ro property does not change after set */
-    ret = tag_cache.c == '1';
-  } else if (lock()) {
-    struct cache_char temp_cache = {{NULL, 0xFFFFFFFF}, '\0'};
-    refresh_cache(&temp_cache, key);
-    ret = temp_cache.c == '1';
-  } else {
-    int change_detected = check_cache(&tag_cache.cache);
-    uint32_t current_serial = __system_property_area_serial();
-    if (current_serial != serial) {
-      change_detected = 1;
-    }
-    if (change_detected) {
-      refresh_cache(&tag_cache, key);
-      serial = current_serial;
-    }
-    ret = tag_cache.c == '1';
-
-    unlock();
-  }
-
-  return ret;
+  return is_debuggable;
 }
 
 /*