make FilePath:IsParent use case-insensitive compare for drive letters on windows

base/file_path.h

Index: base/file_path.h
diff --git a/base/file_path.h b/base/file_path.h
index 5fe8cda8702cb5878c0b12cc51871f97af822d88..17653d1607f6efed37fb6a54479601b5a4d5e714 100644
--- a/base/file_path.h
+++ b/base/file_path.h
@@ -122,13 +122,9 @@ class FilePath {
     return *this;
   }
 
-  bool operator==(const FilePath& that) const {
-    return path_ == that.path_;
-  }
+  bool operator==(const FilePath& that) const;
 
-  bool operator!=(const FilePath& that) const {
-    return path_ != that.path_;
-  }
+  bool operator!=(const FilePath& that) const;
 
   // Required for some STL containers and operations
   bool operator<(const FilePath& that) const {