Make SkString movable.

src/core/SkString.cpp

Index: src/core/SkString.cpp
diff --git a/src/core/SkString.cpp b/src/core/SkString.cpp
index b5655e0503be9574f93047dc54f9158b343c25fc..8ac56744747049479a004de6308aba901e97c2e2 100644
--- a/src/core/SkString.cpp
+++ b/src/core/SkString.cpp
@@ -275,6 +275,13 @@ SkString::SkString(const SkString& src) {
     fRec = RefRec(src.fRec);
 }
 
+SkString::SkString(SkString&& src) {
+    src.validate();
+
+    fRec = src.fRec;
+    src.fRec = const_cast<Rec*>(&gEmptyRec);
+}
+
 SkString::~SkString() {
     this->validate();
 
@@ -310,6 +317,15 @@ SkString& SkString::operator=(const SkString& src) {
     return *this;
 }
 
+SkString& SkString::operator=(SkString&& src) {
+    this->validate();
+
+    if (fRec != src.fRec) {
+        this->swap(src);
+    }
+    return *this;
+}
+
 SkString& SkString::operator=(const char text[]) {
     this->validate();