Make SkTDArray accessors const-friendly

include/core/SkTDArray.h

Index: include/core/SkTDArray.h
===================================================================
--- include/core/SkTDArray.h	(revision 7881)
+++ include/core/SkTDArray.h	(working copy)
@@ -102,16 +102,26 @@
      */
     size_t bytes() const { return fCount * sizeof(T); }
 
-    T*  begin() const { return fArray; }
-    T*  end() const { return fArray ? fArray + fCount : NULL; }
-    T&  operator[](int index) const {
+    T*  begin() { return fArray; }
+    const T*  begin() const { return fArray; }
+    T*  end() { return fArray ? fArray + fCount : NULL; }
+    const T*  end() const { return fArray ? fArray + fCount : NULL; }
+
+    T&  operator[](int index) {
         SkASSERT((unsigned)index < fCount);
         return fArray[index];
     }
+    const T&  operator[](int index) const {
+        SkASSERT((unsigned)index < fCount);
+        return fArray[index];
+    }
 
-    T&  getAt(int index) const {
+    T&  getAt(int index)  {
         return (*this)[index];
     }
+    const T&  getAt(int index) const {
+        return (*this)[index];
+    }
 
     void reset() {
         if (fArray) {
@@ -306,7 +316,7 @@
         this->reset();
     }
 
-    void visitAll(void visitor(T&)) const {
+    void visitAll(void visitor(T&)) {
         T* stop = this->end();
         for (T* curr = this->begin(); curr < stop; curr++) {
             if (*curr) {