Move assert.h/assert.cc from runtime/vm to runtime/platform

runtime/bin/file_linux.cc

Index: runtime/bin/file_linux.cc
diff --git a/runtime/bin/file_linux.cc b/runtime/bin/file_linux.cc
index 00a0e4ec22335ca191136b5138c731426e875772..054e310ad731033e441d1b7a428443dc86e6396b 100644
--- a/runtime/bin/file_linux.cc
+++ b/runtime/bin/file_linux.cc
@@ -158,7 +158,7 @@ char* File::GetCanonicalPath(const char* pathname) {
     do {
       abs_path = realpath(pathname, NULL);
     } while (abs_path == NULL && errno == EINTR);
-    assert(abs_path == NULL || IsAbsolutePath(abs_path));
+    ASSERT(abs_path == NULL || IsAbsolutePath(abs_path));
   }
   return abs_path;
 }