Use explicit WebString <-> string16 conversion methods in storage API files

third_party/WebKit/public/platform/WebString.h

Index: third_party/WebKit/public/platform/WebString.h
diff --git a/third_party/WebKit/public/platform/WebString.h b/third_party/WebKit/public/platform/WebString.h
index 63d3d559bd7b032469e9657a0133116b4b563b2b..5c1c5406f5af30f85631655cc9ba0340752e8d1c 100644
--- a/third_party/WebKit/public/platform/WebString.h
+++ b/third_party/WebKit/public/platform/WebString.h
@@ -72,6 +72,7 @@ namespace blink {
 //
 // * GURL WebStringToGURL(const WebString&)
 // * base::FilePath WebStringToFilePath(const WebString&)
+// * WebString FilePathToWebString(const base::FilePath&);
 //
 // It is inexpensive to copy a WebString object.
 // WARNING: It is not safe to pass a WebString across threads!!!