Fix an exception in the ref counted data. This appeares as a crash on startip

onm my profile because I have a bookmarked favicon that exists but is empty.
This makes the front() behavior of RefCountedBytes the same as
RefCountedStaticMemory, and I documented this as the correct behavior.

TEST=none
BUG=none
Review URL: http://codereview.chromium.org/333048

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@30205 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 7 insertions, 2 deletions

diff --git a/base/ref_counted_memory.h b/base/ref_counted_memory.h
index ef05abd..30d2917 100644
--- a/base/ref_counted_memory.h
+++ b/base/ref_counted_memory.h
@@ -19,7 +19,8 @@ class RefCountedMemory : public base::RefCountedThreadSafe< RefCountedMemory > {
  public:
   virtual ~RefCountedMemory() {}
 
-  // Retrieves a pointer to the beginning of the data we point to.
+  // Retrieves a pointer to the beginning of the data we point to. If the data
+  // is empty, this will return NULL.
   virtual const unsigned char* front() const = 0;
 
   // Size of the memory pointed to.
@@ -64,7 +65,11 @@ class RefCountedBytes : public RefCountedMemory {
   RefCountedBytes(const std::vector<unsigned char>& initializer)
       : data(initializer) {}
 
-  virtual const unsigned char* front() const { return &data.front(); }
+  virtual const unsigned char* front() const {
+    // STL will assert if we do front() on an empty vector, but calling code
+    // expects a NULL.
+    return size() ? &data.front() : NULL;
+  }
   virtual size_t size() const { return data.size(); }
 
   std::vector<unsigned char> data;