Add a histogram (Net.PacResultForStrippedUrl) that estimates how often PAC scripts depend on the UR…

net/proxy/proxy_resolver_v8_tracing.h

Index: net/proxy/proxy_resolver_v8_tracing.h
diff --git a/net/proxy/proxy_resolver_v8_tracing.h b/net/proxy/proxy_resolver_v8_tracing.h
index f5f66cf7486797d0c6282f7dab361b2942cfa283..4ca3c82aac6e87691523ba70579258f4015f00cf 100644
--- a/net/proxy/proxy_resolver_v8_tracing.h
+++ b/net/proxy/proxy_resolver_v8_tracing.h
@@ -89,6 +89,55 @@ class NET_EXPORT ProxyResolverV8TracingFactory {
   DISALLOW_COPY_AND_ASSIGN(ProxyResolverV8TracingFactory);
 };
 
+// This enum is used by an UMA histogram, so the values shouldn't be reordered
+// or renumbered.
+//
+// TODO(eroman): Remove when done gathering data for crbug.com/593759
+enum class PacResultForStrippedUrl {
+  // Did NOT measure the impact of running FindProxyForURL() with a modified
+  // URL path, because the original URL could not complete using the
+  // non-blocking DNS mode.
+  SKIPPED_FALLBACK_BLOCKING_DNS = 0,
+
+  // The result of running FindProxyForURL() with a modified URL path appears
+  // to be indistinguishable. (Although there may have been sideffects to the
+  // script state that won't manifest until later invocations).
+  SUCCESS = 1,
+
+  // Calling FindProxyForURL() with a modified URL path returned the same proxy
+  // list, but had measurable sideffects in calls to alert().
+  SUCCESS_DIFFERENT_ALERTS = 2,
+
+  // Calling FindProxyForURL() with a modified URL path returned the same proxy
+  // list, but invoked a different sequence of DNS resolutions. This would
+  // require a rather unusual script to trigger.
+  SUCCESS_DIFFERENT_NUM_DNS = 3,
+
+  // Calling FindProxyForURL() with a modified URL path resulted in a different
+  // set of DNS dependencies.
+  FAIL_ABANDONED = 4,
+
+  // Calling FindProxyForURL() with a modified URL path caused a different
+  // execution flow. Whereas with the original URL it succeeded with
+  // non-blocking DNS, this attempt requires fallback to blocking DNS (and was
+  // not attempted).
+  FAIL_FALLBACK_BLOCKING_DNS = 5,
+
+  // Calling FindProxyForURL() with a modified URL path caused a script error.
+  FAIL_ERROR = 6,
+
+  // Calling FindProxyForURL() with a modified URL path returned a different
+  // proxy list.
+  FAIL_DIFFERENT_PROXY_LIST = 7,
+
+  MAX_VALUE,
+};
+
+// TODO(eroman): Remove when done gathering data for crbug.com/593759
+//
+// This histogram name is exported only for the sake of unit-tests.
+extern NET_EXPORT_PRIVATE const char kHistogramPacResultForStrippedUrl[];
+
 }  // namespace net
 
 #endif  // NET_PROXY_PROXY_RESOLVER_V8_TRACING_H_