Fix DCHECK() failure when about:memory used.

BUG=28358
TEST=On a debug build (on any platform), go to about:memory and make sure it doesn't fail a DCHECK().

Review URL: http://codereview.chromium.org/418022

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@32677 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 21 insertions, 14 deletions

diff --git a/chrome/browser/browser_about_handler.cc b/chrome/browser/browser_about_handler.cc
index ad517f3..44fab78 100644
--- a/chrome/browser/browser_about_handler.cc
+++ b/chrome/browser/browser_about_handler.cc
@@ -136,11 +136,14 @@ class AboutSource : public ChromeURLDataManager::DataSource {
   DISALLOW_COPY_AND_ASSIGN(AboutSource);
 };
 
-// Handling about:memory is complicated enough to encapsulate it's
-// related methods into a single class.
+// Handling about:memory is complicated enough to encapsulate its related
+// methods into a single class. The user should create it (on the heap) and call
+// its |StartFetch()| method.
 class AboutMemoryHandler : public MemoryDetails {
  public:
-  AboutMemoryHandler(AboutSource* source, int request_id);
+  AboutMemoryHandler(AboutSource* source, int request_id)
+    : source_(source), request_id_(request_id) {}
+
 
   virtual void OnDetailsAvailable();
 
@@ -270,8 +273,11 @@ std::string AboutHistograms(const std::string& query) {
 }
 
 void AboutMemory(AboutSource* source, int request_id) {
-  // The AboutMemoryHandler cleans itself up.
-  new AboutMemoryHandler(source, request_id);
+  // The AboutMemoryHandler cleans itself up, but |StartFetch()| will want the
+  // refcount to be greater than 0.
+  scoped_refptr<AboutMemoryHandler>
+      handler(new AboutMemoryHandler(source, request_id));
+  handler->StartFetch();
 }
 
 std::string AboutObjects(const std::string& query) {
@@ -663,12 +669,6 @@ void AboutSource::FinishDataRequest(const std::string& response,
 
 // AboutMemoryHandler ----------------------------------------------------------
 
-AboutMemoryHandler::AboutMemoryHandler(AboutSource* source, int request_id)
-  : source_(source),
-    request_id_(request_id) {
-  StartFetch();
-}
-
 // Helper for AboutMemory to bind results from a ProcessMetrics object
 // to a DictionaryValue. Fills ws_usage and comm_usage so that the objects
 // can be used in caller's scope (e.g for appending to a net total).
diff --git a/chrome/browser/memory_details.h b/chrome/browser/memory_details.h
index bfee58e..21af097 100644
--- a/chrome/browser/memory_details.h
+++ b/chrome/browser/memory_details.h
@@ -64,14 +64,21 @@ class ProcessInfoSnapshot;
 //
 //    class MyMemoryDetailConsumer : public MemoryDetails {
 //
-//      MyMemoryDetailConsumer() : MemoryDetails(true) {
+//      MyMemoryDetailConsumer() {
+//        // Anything but |StartFetch()|.
+//      }
+//
+//      // (Or just call |StartFetch()| explicitly if there's nothing else to
+//      // do.)
+//      void StartDoingStuff() {
 //        StartFetch();  // Starts fetching details.
+//        // Etc.
 //      }
 //
-//      // Your class stuff here
+//      // Your other class stuff here
 //
 //      virtual void OnDetailsAvailable() {
-//           // do work with memory info here
+//        // do work with memory info here
 //      }
 //    }
 class MemoryDetails : public base::RefCountedThreadSafe<MemoryDetails> {