Add support for building the Dart VM for Android OS.

runtime/bin/directory_android.cc

Index: runtime/bin/directory_android.cc
diff --git a/runtime/bin/directory_posix.cc b/runtime/bin/directory_android.cc
similarity index 92%
copy from runtime/bin/directory_posix.cc
copy to runtime/bin/directory_android.cc
index 7adb80f9156ab2d308131aee2181243b35b85a27..2bad45620e8f2ffa012c6711a0db599de47ebd5f 100644
--- a/runtime/bin/directory_posix.cc
+++ b/runtime/bin/directory_android.cc
@@ -376,7 +376,15 @@ Directory::ExistsResult Directory::Exists(const char* dir_name) {
 
 
 char* Directory::Current() {
-  return getcwd(NULL, 0);
+  // Android's getcwd adheres closely to the POSIX standard. It won't
+  // allocate memory. We need to make our own copy.
+
+  char buffer[PATH_MAX];
+  if (NULL == getcwd(buffer, PATH_MAX)) {
+    return NULL;
+  }
+
+  return strdup(buffer);
 }
 
 
@@ -387,6 +395,18 @@ bool Directory::Create(const char* dir_name) {
 }
 
 
+// Android doesn't currently provide mkdtemp
+static char* Mkdtemp(char* path_template) {
+  if (mktemp(path_template) == NULL) {
+    return NULL;
+  }
+  if (mkdir(path_template, 0700) != 0) {
+    return NULL;
+  }
+  return path_template;
+}
+
+
 char* Directory::CreateTemp(const char* const_template) {
   // Returns a new, unused directory name, modifying the contents of
   // dir_template.  Creates the directory with the permissions specified
@@ -402,11 +422,22 @@ char* Directory::CreateTemp(const char* const_template) {
       snprintf(path + path_length, PATH_MAX - path_length, "XXXXXX");
     }
   } else {
-    snprintf(path, PATH_MAX, "/tmp/temp_dir1_XXXXXX");
+    // Android does not have a /tmp directory. A partial substitute,
+    // suitable for bring-up work and tests, is to create a tmp
+    // directory in /data/local/tmp.
+    //
+    // TODO(4413): In the long run, when running in an application we should
+    // probably use android.content.Context.getCacheDir().
+    #define ANDROID_TEMP_DIR "/data/local/tmp"
+    struct stat st;
+    if (stat(ANDROID_TEMP_DIR, &st) != 0) {
+      mkdir(ANDROID_TEMP_DIR, 0777);
+    }
+    snprintf(path, PATH_MAX, ANDROID_TEMP_DIR "/temp_dir1_XXXXXX");
   }
   char* result;
   do {
-    result = mkdtemp(path);
+    result = Mkdtemp(path);
   } while (result == NULL && errno == EINTR);
   if (result == NULL) {
     free(path);