Implement FilePath::Contains()

base/file_path.cc

Index: base/file_path.cc
diff --git a/base/file_path.cc b/base/file_path.cc
index a938ca63c7ec5b78726cd4c34e0b54c49707feba..b88d1e80937135adab33a656a09380584e9d474c 100644
--- a/base/file_path.cc
+++ b/base/file_path.cc
@@ -3,11 +3,13 @@
 // found in the LICENSE file.
 
 #include "base/file_path.h"
+#include "base/file_util.h"
 #include "base/logging.h"
 
 // These includes are just for the *Hack functions, and should be removed
 // when those functions are removed.
 #include "base/string_piece.h"
+#include "base/string_util.h"
 #include "base/sys_string_conversions.h"
 
 #if defined(FILE_PATH_USES_WIN_SEPARATORS)
@@ -178,6 +180,31 @@ bool FilePath::IsAbsolute() const {
   return IsPathAbsolute(path_);
 }
 
+bool FilePath::Contains(const FilePath &other) const {
+  FilePath parent = FilePath(*this);
+  FilePath child = FilePath(other);
+
+  if (!file_util::AbsolutePath(&parent) || !file_util::AbsolutePath(&child))
+    return false;
+
+#if defined(OS_WIN)
+  // file_util::AbsolutePath() does not flatten case on Windows, so we must do
+  // a case-insensitive compare.
+  if (!StartsWith(child.value(), parent.value(), false))
+#else
+  if (!StartsWithASCII(child.value(), parent.value(), true))
+#endif
+    return false;
+
+  // file_util::AbsolutePath() normalizes '/' to '\', so we only need to check
+  // kSeparators[0].
+  if (child.value().length() <= parent.value().length() ||
+      child.value()[parent.value().length()] != kSeparators[0])
+    return false;
+
+  return true;
+}
+
 #if defined(OS_POSIX)
 // See file_path.h for a discussion of the encoding of paths on POSIX
 // platforms.  These *Hack() functions are not quite correct, but they're