Move String::truncate to StringImpl.

String should be a thin wrapper over StringImpl and other functions.

Review-Url: https://codereview.chromium.org/2337683002
Cr-Commit-Position: refs/heads/master@{#419095}

third_party/WebKit/Source/wtf/text/StringImpl.cpp

@@ -897,6 +897,15 @@ PassRefPtr<StringImpl> StringImpl::foldCase()
     return newImpl.release();
 }
 
+PassRefPtr<StringImpl> StringImpl::truncate(unsigned length)
+{
+    if (length >= m_length)
+        return this;
+    if (is8Bit())
+        return create(characters8(), length);
+    return create(characters16(), length);
+}
+
 template <class UCharPredicate>
 inline PassRefPtr<StringImpl> StringImpl::stripMatchedCharacters(UCharPredicate predicate)
 {

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

@@ -338,6 +338,8 @@ public:
     // FIXME: Do we need fill(char) or can we just do the right thing if UChar is ASCII?
     PassRefPtr<StringImpl> foldCase();
 
+    PassRefPtr<StringImpl> truncate(unsigned length);
+
     PassRefPtr<StringImpl> stripWhiteSpace();
     PassRefPtr<StringImpl> stripWhiteSpace(IsWhiteSpaceFunctionPtr);
     PassRefPtr<StringImpl> simplifyWhiteSpace(StripBehavior = StripExtraWhiteSpace);

third_party/WebKit/Source/wtf/text/WTFString.cpp

@@ -231,21 +231,10 @@ void String::ensure16Bit()
         m_impl = StringImpl::empty16Bit();
 }
 
-void String::truncate(unsigned position)
+void String::truncate(unsigned length)
 {
-    if (position >= length())
-        return;
-    if (m_impl->is8Bit()) {
-        LChar* data;
-        RefPtr<StringImpl> newImpl = StringImpl::createUninitialized(position, data);
-        memcpy(data, m_impl->characters8(), position * sizeof(LChar));
-        m_impl = newImpl.release();
-    } else {
-        UChar* data;
-        RefPtr<StringImpl> newImpl = StringImpl::createUninitialized(position, data);
-        memcpy(data, m_impl->characters16(), position * sizeof(UChar));
-        m_impl = newImpl.release();
-    }
+    if (m_impl)
+        m_impl = m_impl->truncate(length);
 }
 
 void String::remove(unsigned start, unsigned lengthToRemove)

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

@@ -246,7 +246,7 @@ public:
 
     void ensure16Bit();
 
-    void truncate(unsigned len);
+    void truncate(unsigned length);
     void remove(unsigned start, unsigned length = 1);
 
     String substring(unsigned pos, unsigned len = UINT_MAX) const;