HTTP Cache: Implement StopCaching(), to avoid caching

net/http/http_cache_transaction.cc

Index: net/http/http_cache_transaction.cc
===================================================================
--- net/http/http_cache_transaction.cc	(revision 110637)
+++ net/http/http_cache_transaction.cc	(working copy)
@@ -183,7 +183,7 @@
 }
 
 bool HttpCache::Transaction::AddTruncatedFlag() {
-  DCHECK(mode_ & WRITE);
+  DCHECK(mode_ & WRITE || mode_ == NONE);
 
   // Don't set the flag for sparse entries.
   if (partial_.get() && !truncated_)
@@ -362,6 +362,16 @@
 }
 
 void HttpCache::Transaction::StopCaching() {
+  // We really don't know where we are now. Hopefully there is no operation in
+  // progress, but nothing really prevents this method to be called after we
+  // returned ERR_IO_PENDING. We cannot attempt to truncate the entry at this
+  // point because we need the state machine for that (and even if we are really
+  // free, that would be an asynchronous operation). In other words, keep the
+  // entry how it is (it will be marked as truncated at destruction), and let
+  // the next piece of code that executes know that we are now reading directly
+  // from the net.
+  if (cache_ && entry_ && (mode_ & WRITE))
+    mode_ = NONE;
 }
 
 void HttpCache::Transaction::DoneReading() {
@@ -794,9 +804,9 @@
   if (!cache_)
     return ERR_UNEXPECTED;
 
-  // If there is an error and we are saving the data, just tell the user about
-  // it and wait until the destructor runs to see if we can keep the data.
-  if (mode_ != NONE && result < 0)
+  // If there is an error or we aren't saving the data, we are done; just wait
+  // until the destructor runs to see if we can keep the data.
+  if (mode_ == NONE || result < 0)
     return result;
 
   next_state_ = STATE_CACHE_WRITE_DATA;