Bug 1180715 (1/4) - Track image LoadTime to compare with file mtime. review=seth

mTouchedTime is not appropriate for this as it is updated when an image
load re-uses the same imgRequest, especially as it has one second
granularity. A timestamp that is updated every time the backing file is
re-read should work better.

A millisecond granularity timestamp would be preferable, and would be
achievable on most or all supported platforms. But some older
filesystems have timestamp granularity of a second or worse, notably
ext3 and FAT32 (and even ext4 filesytems created with inode_size < 256
bytes, e.g. with 'mke2fs -t small' - see
https://ext4.wiki.kernel.org/index.php/Ext4_Disk_Layout#Inode_Timestamps
for details.)

image/imgLoader.cpp

@@ -862,6 +862,7 @@ imgCacheEntry::imgCacheEntry(imgLoader* loader, imgRequest* request,
    mRequest(request),
    mDataSize(0),
    mTouchedTime(SecondsFromPRTime(PR_Now())),
+   mLoadTime(SecondsFromPRTime(PR_Now())),
    mExpiryTime(0),
    mMustValidate(false),
    // We start off as evicted so we don't try to update the cache. PutIntoCache
@@ -898,6 +899,11 @@ imgCacheEntry::UpdateCache(int32_t diff /* = 0 */)
   }
 }
 
+void imgCacheEntry::UpdateLoadTime()
+{
+  mLoadTime = SecondsFromPRTime(PR_Now());
+}
+
 void
 imgCacheEntry::SetHasNoProxies(bool hasNoProxies)
 {
@@ -1710,7 +1716,7 @@ imgLoader::ValidateEntry(imgCacheEntry* aEntry,
   // Special treatment for file URLs - aEntry has expired if file has changed
   nsCOMPtr<nsIFileURL> fileUrl(do_QueryInterface(aURI));
   if (fileUrl) {
-    uint32_t lastModTime = aEntry->GetTouchedTime();
+    uint32_t lastModTime = aEntry->GetLoadTime();
 
     nsCOMPtr<nsIFile> theFile;
     rv = fileUrl->GetFile(getter_AddRefs(theFile));

image/imgLoader.h

@@ -91,6 +91,13 @@ public:
     Touch(/* updateTime = */ false);
   }
 
+  uint32_t GetLoadTime() const
+  {
+    return mLoadTime;
+  }
+
+  void UpdateLoadTime();
+
   int32_t GetExpiryTime() const
   {
     return mExpiryTime;
@@ -164,6 +171,7 @@ private: // data
   RefPtr<imgRequest> mRequest;
   uint32_t mDataSize;
   int32_t mTouchedTime;
+  uint32_t mLoadTime;
   int32_t mExpiryTime;
   nsExpirationState mExpirationState;
   bool mMustValidate : 1;

image/imgRequest.cpp

@@ -159,6 +159,7 @@ imgRequest::Init(nsIURI *aURI,
   mChannel->SetNotificationCallbacks(this);
 
   mCacheEntry = aCacheEntry;
+  mCacheEntry->UpdateLoadTime();
 
   SetLoadId(aCX);