base: "implement" seek time detection for iOS/Android and add more stubs.

base/sys_info_posix.cc

Index: base/sys_info_posix.cc
diff --git a/base/sys_info_posix.cc b/base/sys_info_posix.cc
index cdb95d78d4434fb977f247352b7e73503da6f8f2..3d49bf94da925d9032ecdefdb181ed6bc08bf38f 100644
--- a/base/sys_info_posix.cc
+++ b/base/sys_info_posix.cc
@@ -96,10 +96,6 @@ int64 SysInfo::AmountOfFreeDiskSpace(const FilePath& path) {
   return static_cast<int64>(stats.f_bavail) * stats.f_frsize;
 }
 
-bool SysInfo::HasSeekPenalty(const FilePath& path, bool* has_seek_penalty) {
-  return false;
-}
-
 #if !defined(OS_MACOSX) && !defined(OS_ANDROID)
 // static
 std::string SysInfo::OperatingSystemName() {