Rename non-const payload() in base::Pickle to mutable_pyload()

base::Pickle has two methods - one is declared const and another one is not.
The non const version of the method is protected, which makes the const
payload() inaccessible in non-const Pickle instances.
Also made end_of_payload() public and removed non-const version of that method.

Review URL: https://codereview.chromium.org/11959022

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@177711 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/base/pickle.h b/base/pickle.h
index cd587de..62dcd15 100644
--- a/base/pickle.h
+++ b/base/pickle.h
@@ -278,26 +278,23 @@
 
   // The payload is the pickle data immediately following the header.
   size_t payload_size() const { return header_->payload_size; }
+
   const char* payload() const {
     return reinterpret_cast<const char*>(header_) + header_size_;
   }
 
- protected:
-  char* payload() {
-    return reinterpret_cast<char*>(header_) + header_size_;
-  }
-
   // Returns the address of the byte immediately following the currently valid
   // header + payload.
-  char* end_of_payload() {
-    // We must have a valid header_.
-    return payload() + payload_size();
-  }
   const char* end_of_payload() const {
     // This object may be invalid.
     return header_ ? payload() + payload_size() : NULL;
   }
 
+ protected:
+  char* mutable_payload() {
+    return reinterpret_cast<char*>(header_) + header_size_;
+  }
+
   size_t capacity() const {
     return capacity_;
   }