Handle URLRequest::Read() returning false without an error or ERR_IO_PENDING.

This is a possible cause for a failure being seen in the field in the
associated bug; this change is a quick fix for that failure + UMA to
determine if the failure is real.

BUG=416639
R=mef@chromium.org
R=asvitkine@chromium.org

Review URL: https://codereview.chromium.org/597633002

Cr-Commit-Position: refs/heads/master@{#296241}

net/base/sdch_dictionary_fetcher.cc

@@ -204,6 +204,14 @@ int SdchDictionaryFetcher::DoRead(int rv) {
       return ERR_IO_PENDING;
 
     DCHECK_NE(current_request_->status().error(), OK);
+    if (current_request_->status().error() == OK) {
+      // This "should never happen", but if it does the result will be
+      // an infinite loop.  It's not clear how to handle a read failure
+      // without a promise to invoke the callback at some point in the future,
+      // so the request is failed.
+      SdchManager::SdchErrorRecovery(SdchManager::DICTIONARY_FETCH_READ_FAILED);
+      return ERR_FAILED;
+    }
 
     return current_request_->status().error();
   }

net/base/sdch_manager.h

@@ -124,6 +124,7 @@ class NET_EXPORT SdchManager
     DICTIONARY_COUNT_EXCEEDED = 35,
     DICTIONARY_ALREADY_SCHEDULED_TO_DOWNLOAD = 36,
     DICTIONARY_ALREADY_TRIED_TO_DOWNLOAD = 37,
+    DICTIONARY_FETCH_READ_FAILED = 38,
 
     // Failsafe hack.
     ATTEMPT_TO_DECODE_NON_HTTP_DATA = 40,

tools/metrics/histograms/histograms.xml

@@ -50141,6 +50141,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="35" label="DICTIONARY_COUNT_EXCEEDED"/>
   <int value="36" label="DICTIONARY_ALREADY_SCHEDULED_TO_DOWNLOAD"/>
   <int value="37" label="DICTIONARY_ALREADY_TRIED_TO_DOWNLOAD"/>
+  <int value="38" label="DICTIONARY_FETCH_READ_FAILED"/>
   <int value="40" label="ATTEMPT_TO_DECODE_NON_HTTP_DATA"/>
   <int value="50" label="MULTIENCODING_FOR_NON_SDCH_REQUEST"/>
   <int value="51" label="SDCH_CONTENT_ENCODE_FOR_NON_SDCH_REQUEST"/>