Avoid MemoryCache eviction of preloaded resources with devtools open

third_party/WebKit/Source/core/fetch/MemoryCache.cpp

Index: third_party/WebKit/Source/core/fetch/MemoryCache.cpp
diff --git a/third_party/WebKit/Source/core/fetch/MemoryCache.cpp b/third_party/WebKit/Source/core/fetch/MemoryCache.cpp
index cc8f4aa88283184ec11c38ae5054fc5643075ebc..b84a99f14b6f42f222d26efdf60e20da042f0d62 100644
--- a/third_party/WebKit/Source/core/fetch/MemoryCache.cpp
+++ b/third_party/WebKit/Source/core/fetch/MemoryCache.cpp
@@ -627,19 +627,29 @@ MemoryCache::Statistics MemoryCache::getStatistics() {
   return stats;
 }
 
-void MemoryCache::evictResources() {
-  while (true) {
-    ResourceMapIndex::iterator resourceMapIter = m_resourceMaps.begin();
-    if (resourceMapIter == m_resourceMaps.end())
-      break;
+void MemoryCache::evictResources(EvictResourcePolicy policy) {
+  for (auto resourceMapIter = m_resourceMaps.begin();
+       resourceMapIter != m_resourceMaps.end();) {
     ResourceMap* resources = resourceMapIter->value.get();
-    while (true) {
-      ResourceMap::iterator resourceIter = resources->begin();
-      if (resourceIter == resources->end())
-        break;
-      evict(resourceIter->value.get());
+    for (auto resourceIter = resources->begin();
+         resourceIter != resources->end();) {
+      DCHECK(resourceIter.get());
+      DCHECK(resourceIter->value.get());
+      DCHECK(resourceIter->value->resource());
+      if (policy == EvictAllResources || !resourceIter->value->resource() ||

[Charlie Harrison, 2016/10/03 21:48:21]

Optional nit: I think !(resourceIter->value->resource() &&
resourceIter->value->resource()->isUnusedPreload()) is clearer as an explicit
null check.

+          !resourceIter->value->resource()->isUnusedPreload()) {
+        evict(resourceIter->value.get());
+        resourceIter = resources->begin();

[Charlie Harrison, 2016/10/03 21:48:21]

Hm... If we have N unused preloads, and then M regular resources, wouldn't this
loop have N * M iterations? I wonder if we can do something smarter about
incrementing the iterator so it doesn't just go back to the beginning. 

 Can we increment the iterator before we evict the resource? I don't think
iterators to other elements in a map are invalidated on erasure for STL maps,
but I'm not sure about WTF.

+      } else {
+        ++resourceIter;
+      }
+    }
+    if (!resources->size()) {
+      m_resourceMaps.remove(resourceMapIter);
+      resourceMapIter = m_resourceMaps.begin();
+    } else {
+      ++resourceMapIter;
     }
-    m_resourceMaps.remove(resourceMapIter);
   }
 }