Provide base::EvictFileFromSystemCache on Android on ARM32

This is needed to be able to run disk_cache_perftest on the platform.

This just uses the Linux implementation, but provides a syscall wrapper
since NDK won't provide one at the API level we build for.

BUG=722885

Review-Url: https://codereview.chromium.org/2885423002
Cr-Commit-Position: refs/heads/master@{#476281}

base/test/BUILD.gn

@@ -196,6 +196,9 @@ static_library("test_support") {
   }
 
   if (is_android) {
+    set_sources_assignment_filter([])
+    sources += [ "test_file_util_linux.cc" ]
+    set_sources_assignment_filter(sources_assignment_filter)
     deps += [
       ":base_unittests_jni_headers",
       ":test_support_jni_headers",

base/test/test_file_util_linux.cc

@@ -9,11 +9,42 @@
 #include <sys/types.h>
 #include <unistd.h>
 
+#if defined(OS_ANDROID)
+#include <asm/unistd.h>
+#include <errno.h>
+#include <linux/fadvise.h>
+#include <sys/syscall.h>
+#endif
+
 #include "base/files/file_path.h"
 #include "base/files/scoped_file.h"
 
 namespace base {
 
+// Inconveniently, the NDK doesn't provide for posix_fadvise
+// until native API level = 21, which we don't use yet, so provide a wrapper, at
+// least on ARM32
+#if defined(OS_ANDROID) && __ANDROID_API__ < 21
+
+namespace {
+int posix_fadvise(int fd, off_t offset, off_t len, int advice) {
+#if defined(ARCH_CPU_ARMEL)
+  // Note that the syscall argument order on ARM is different from the C
+  // function; this is helpfully documented in the Linux posix_fadvise manpage.
+  return syscall(__NR_arm_fadvise64_64, fd, advice,
+                 0,  // Upper 32-bits for offset
+                 offset,
+                 0,  // Upper 32-bits for length
+                 len);
+#endif
+  NOTIMPLEMENTED();
+  return ENOSYS;
+}
+
+}  // namespace
+
+#endif  // OS_ANDROID
+
 bool EvictFileFromSystemCache(const FilePath& file) {
   ScopedFD fd(open(file.value().c_str(), O_RDONLY));
   if (!fd.is_valid())

base/test/test_file_util_posix.cc

@@ -79,7 +79,7 @@ bool DieFileDie(const FilePath& file, bool recurse) {
   return DeleteFile(file, recurse);
 }
 
-#if !defined(OS_LINUX) && !defined(OS_MACOSX)
+#if !defined(OS_LINUX) && !defined(OS_MACOSX) && !defined(OS_ANDROID)
 bool EvictFileFromSystemCache(const FilePath& file) {
   // There doesn't seem to be a POSIX way to cool the disk cache.
   NOTIMPLEMENTED();