Expand WTF::StringView's API to be more like StringPiece.

third_party/WebKit/Source/wtf/text/AtomicString.h

Index: third_party/WebKit/Source/wtf/text/AtomicString.h
diff --git a/third_party/WebKit/Source/wtf/text/AtomicString.h b/third_party/WebKit/Source/wtf/text/AtomicString.h
index 6fb8300e67062230c00ff1608739dbda098d2f12..41c778a4fe32bba9255661b932ededbd93f61816 100644
--- a/third_party/WebKit/Source/wtf/text/AtomicString.h
+++ b/third_party/WebKit/Source/wtf/text/AtomicString.h
@@ -25,6 +25,7 @@
 #include "wtf/HashTableDeletedValueType.h"
 #include "wtf/WTFExport.h"
 #include "wtf/text/CString.h"
+#include "wtf/text/StringView.h"
 #include "wtf/text/WTFString.h"
 #include <cstring>
 #include <iosfwd>
@@ -233,6 +234,13 @@ inline AtomicString AtomicString::fromUTF8(const char* characters)
     return fromUTF8Internal(characters, 0);
 }
 
+inline StringView::StringView(const AtomicString& string)
+    : StringView(string, 0, string.length()) {}
+inline StringView::StringView(const AtomicString& string, unsigned offset, unsigned length)
+    : StringView(string.impl(), offset, length) {}
+inline StringView::StringView(const AtomicString& string, unsigned offset)
+    : StringView(string.impl(), offset) {}
+
 // AtomicStringHash is the default hash for AtomicString
 template<typename T> struct DefaultHash;
 template<> struct DefaultHash<AtomicString> {