[tracing] Add WebCache memory usage in Blink to chrome://tracing

components/web_cache/browser/web_cache_manager.h

Index: components/web_cache/browser/web_cache_manager.h
diff --git a/components/web_cache/browser/web_cache_manager.h b/components/web_cache/browser/web_cache_manager.h
index 0d2d3ffb644a6f05234b4e54a06a6390b3007e52..0aba07fa1821c7ea6e943cfa9905f8221298ad90 100644
--- a/components/web_cache/browser/web_cache_manager.h
+++ b/components/web_cache/browser/web_cache_manager.h
@@ -17,6 +17,7 @@
 #include "base/gtest_prod_util.h"
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
+#include "base/trace_event/memory_dump_provider.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "third_party/WebKit/public/web/WebCache.h"
@@ -27,7 +28,8 @@ class PrefRegistrySimple;
 
 namespace web_cache {
 
-class WebCacheManager : public content::NotificationObserver {
+class WebCacheManager : public content::NotificationObserver,
+                        public base::trace_event::MemoryDumpProvider {
   friend class WebCacheManagerTest;
   FRIEND_TEST_ALL_PREFIXES(
       WebCacheManagerTest,
@@ -98,6 +100,10 @@ class WebCacheManager : public content::NotificationObserver {
                const content::NotificationSource& source,
                const content::NotificationDetails& details) override;
 
+  // base::trace_event::MemoryDUmpProvider implementation.
+  bool OnMemoryDump(const base::trace_event::MemoryDumpArgs& args,
+                    base::trace_event::ProcessMemoryDump* pmd) override;
+
   // Gets the default global size limit.  This interrogates system metrics to
   // tune the default size to the current system.
   static size_t GetDefaultGlobalSizeLimit();
@@ -217,6 +223,10 @@ class WebCacheManager : public content::NotificationObserver {
   // Check to see if any active renderers have fallen inactive.
   void FindInactiveRenderers();
 
+  // Helper method to dump the cache usage stats of given renderer.
+  void DumpUsageStats(int renderer_id,
+                      base::trace_event::ProcessMemoryDump* pmd);
+
   // The global size limit for all in-memory caches.
   size_t global_size_limit_;