tools: Local tests for the speculative prefetch predictor.

chrome/browser/predictors/resource_prefetch_common.h

Index: chrome/browser/predictors/resource_prefetch_common.h
diff --git a/chrome/browser/predictors/resource_prefetch_common.h b/chrome/browser/predictors/resource_prefetch_common.h
index 33812ff5183a9975a1ca432698b828bb81cab67c..4495cbbecca651284999f60a350407a487651507 100644
--- a/chrome/browser/predictors/resource_prefetch_common.h
+++ b/chrome/browser/predictors/resource_prefetch_common.h
@@ -69,10 +69,14 @@ struct ResourcePrefetchPredictorConfig {
 
   // The mode the prefetcher is running in. Forms a bit map.
   enum Mode {
-    URL_LEARNING    = 1 << 0,
-    HOST_LEARNING   = 1 << 1,
-    URL_PREFETCHING = 1 << 2,  // Should also turn on URL_LEARNING.
-    HOST_PRFETCHING = 1 << 3   // Should also turn on HOST_LEARNING.
+    URL_LEARNING = 1 << 0,
+    HOST_LEARNING = 1 << 1,
+    URL_PREFETCHING = 1 << 2,   // Should also turn on URL_LEARNING.
+    HOST_PREFETCHING = 1 << 3,  // Should also turn on HOST_LEARNING.
+    // External requests are from a direct call to
+    // ResourcePrefetchPredictor::StartPrefetching(), not from observing
+    // navigation starts.
+    EXTERNAL_ONLY = 1 << 4

[pasko, 2016/11/24 19:31:16]

Non-orthogonal bits are confusing, especially when inferred from combinations of
flags that are non-orthogonal themselves. It is unnecessarily hard to guess what
you wanted. It seems it has some bugs, but perhaps some of those are intentional
behaviors, but hard to tell which ones are shich.

Orthogonal naming I am thinking about:
URL_LEARNING,
HOST_LEARNING,
URL_PREFETCHING_FOR_MAIN_FRAMES,
HOST_PREFETCHING_FOR_MAIN_FRAMES,
URL_PREFETCHING_FOR_EXTERNAL_REQUESTS,
HOST_PREFETCHING_FOR_EXTERNAL_REQUESTS

Disabling prefetch for external requests while keeping prefetch for main frame
requests may also be useful, supporting it would arrive essentially for free.

   };
   int mode;
 
@@ -81,6 +85,7 @@ struct ResourcePrefetchPredictorConfig {
   bool IsPrefetchingEnabled(Profile* profile) const;
   bool IsURLLearningEnabled() const;
   bool IsHostLearningEnabled() const;
+  bool ExternalPrefetchingOnly() const;
   bool IsURLPrefetchingEnabled(Profile* profile) const;
   bool IsHostPrefetchingEnabled(Profile* profile) const;