change SkColorTable to be immutable

include/core/SkBitmap.h

Index: include/core/SkBitmap.h
diff --git a/include/core/SkBitmap.h b/include/core/SkBitmap.h
index 887169ccb522c2820c8c2f0ff3f78e454d0d00cf..07d2b955533b78d37a7ebcb96e3217fd1e8bcb6c 100644
--- a/include/core/SkBitmap.h
+++ b/include/core/SkBitmap.h
@@ -748,7 +748,7 @@ public:
     }
     ~SkAutoLockColors() {
         if (fCTable) {
-            fCTable->unlockColors(false);
+            fCTable->unlockColors();
         }
     }
 
@@ -762,7 +762,7 @@ public:
      */
     const SkPMColor* lockColors(SkColorTable* ctable) {
         if (fCTable) {
-            fCTable->unlockColors(false);
+            fCTable->unlockColors();
         }
         fCTable = ctable;
         fColors = ctable ? ctable->lockColors() : NULL;