Clear SDCH information on "Clear browsing data" path.

chrome/browser/net/sdch_dictionary_fetcher.cc

Index: chrome/browser/net/sdch_dictionary_fetcher.cc
diff --git a/chrome/browser/net/sdch_dictionary_fetcher.cc b/chrome/browser/net/sdch_dictionary_fetcher.cc
index 1130fe336242b5b5c666a2ae433771e1b98d3bd4..dfc64f95442781b43e93b99d1639b8a0b7c57f3a 100644
--- a/chrome/browser/net/sdch_dictionary_fetcher.cc
+++ b/chrome/browser/net/sdch_dictionary_fetcher.cc
@@ -49,6 +49,16 @@ void SdchDictionaryFetcher::Schedule(const GURL& dictionary_url) {
   ScheduleDelayedRun();
 }
 
+void SdchDictionaryFetcher::Cancel() {
+  DCHECK(CalledOnValidThread());
+
+  current_fetch_.reset(NULL);
+  weak_factory_.InvalidateWeakPtrs();
+  attempted_load_.clear();
+  std::queue<GURL> trash_queue;
+  fetch_queue_.swap(trash_queue);

[jar (doing other things), 2014/06/11 23:23:49]

nit: (personal style): It is probably safer to first effectively clear the queue
(via your swap technique), and then invalidate the weak pointers, on the *off*
chance that some side effect of the pointer release would induce reentrant
callbacks which examine or test the queue.

I don't think this happens... but it is a personal style issue which sometimes
has saved me (and failure to do so has historically hurt me in some code). 
YMMV.

[Randy Smith (Not in Mondays), 2014/06/12 18:15:45]

Hmmm.  So your comment made me think about ordering, and the conclusions I came
to were:
* I can't see a way in which invalidating weak pointers can result in
re-entrancy, because invalidating weak pointers breaks links to this class
without affecting ownership or deletion semantics.
* I *could* imagine the reset of the URLFetcher resulting in some interesting
re-entrancy.

So I did the URLFetcher reset last, and did the weak pointer invalidation
second-to-last as per your request/in case I'm missing something.  But I'd be
interested in more details about how you think invalidating weak pointers could
result in re-entrancy if you're willing to share.

+}
+
 void SdchDictionaryFetcher::ScheduleDelayedRun() {
   if (fetch_queue_.empty() || current_fetch_.get() || task_is_pending_)
     return;