Small no-op refactor in HttpCache::Transaction.

Extract the checks that need not be run on each iteration of the loop.
Given the constant size of kValidationHeaders, this does not
meaningfully improve complexity, only readability (hopefully).

Change-Id: Ic14796c1a76426f0bbb3f40247744ba5b98318f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2386739
Commit-Queue: Titouan Rigoudy <titouan@chromium.org>
Reviewed-by: Maksim Orlovich <morlovich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803862}

net/http/http_cache_transaction.cc

@@ -2632,28 +2632,39 @@ int HttpCache::Transaction::ValidateEntryHeadersAndContinue() {
   return OK;
 }
 
-int HttpCache::Transaction::BeginExternallyConditionalizedRequest() {
-  DCHECK_EQ(UPDATE, mode_);
+bool HttpCache::Transaction::
+    ExternallyConditionalizedValidationHeadersMatchEntry() const {
   DCHECK(external_validation_.initialized);
 
   for (size_t i = 0; i < base::size(kValidationHeaders); i++) {
     if (external_validation_.values[i].empty())
       continue;
+
     // Retrieve either the cached response's "etag" or "last-modified" header.
     std::string validator;
     response_.headers->EnumerateHeader(
         nullptr, kValidationHeaders[i].related_response_header_name,
         &validator);
 
-    if (response_.headers->response_code() != 200 || truncated_ ||
-        validator.empty() || validator != external_validation_.values[i]) {
-      // The externally conditionalized request is not a validation request
-      // for our existing cache entry. Proceed with caching disabled.
-      UpdateCacheEntryStatus(CacheEntryStatus::ENTRY_OTHER);
-      DoneWithEntry(true);
+    if (validator != external_validation_.values[i]) {
+      return false;
     }
   }
 
+  return true;
+}
+
+int HttpCache::Transaction::BeginExternallyConditionalizedRequest() {
+  DCHECK_EQ(UPDATE, mode_);
+
+  if (response_.headers->response_code() != 200 || truncated_ ||
+      !ExternallyConditionalizedValidationHeadersMatchEntry()) {
+    // The externally conditionalized request is not a validation request
+    // for our existing cache entry. Proceed with caching disabled.
+    UpdateCacheEntryStatus(CacheEntryStatus::ENTRY_OTHER);
+    DoneWithEntry(true);
+  }
+
   TransitionToState(STATE_SEND_REQUEST);
   return OK;
 }

net/http/http_cache_transaction.h

@@ -381,6 +381,10 @@ class NET_EXPORT_PRIVATE HttpCache::Transaction : public HttpTransaction {
   // the validation of the rest of the entry.  Returns a network error code.
   int ValidateEntryHeadersAndContinue();
 
+  // Returns whether the current externally conditionalized request's validation
+  // headers match the current cache entry's headers.
+  bool ExternallyConditionalizedValidationHeadersMatchEntry() const;
+
   // Called to start requests which were given an "if-modified-since" or
   // "if-none-match" validation header by the caller (NOT when the request was
   // conditionalized internally in response to LOAD_VALIDATE_CACHE).