Improve the image data cache.

Adds a flag to ImageData in the plugin process for whether it's been used in
a ReplaceContents call and only attempt to cache image datas if this flag is
set. Since we only get the "usable" notifications from the renderer for the
ReplaceContents case, all other images can never be re-used so adding them is
a waste.

This also adds a check to avoid immediately overwriting an entry marked usable.
In practice, I don't think this will make a difference with the current code,
since the plugin won't do ReplaceContents faster than we'll get usable
notifications back from the renderer. However, the number of items in-flight
isn't guaranteed so it seems like this is a good margin of safety.

An alternative would have been to do a similar check when adding an entry, and
not replace one that's usable. However, if we make a new GraphicsContext with
a new size, this means that we'll never overwrite an "old"-sized image until
it times out and the cache won't work well. With the current code, it should
replace the old-sized usable entry after two frames instead:

BUG=142507
Review URL: https://chromiumcodereview.appspot.com/10880033

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@153267 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 9 insertions, 2 deletions

diff --git a/ppapi/proxy/ppb_image_data_proxy.h b/ppapi/proxy/ppb_image_data_proxy.h
index 812fd78..046c1ce 100644
--- a/ppapi/proxy/ppb_image_data_proxy.h
+++ b/ppapi/proxy/ppb_image_data_proxy.h
@@ -62,8 +62,11 @@ class ImageData : public ppapi::Resource,
 
   const PP_ImageDataDesc& desc() const { return desc_; }
 
-  // Fills the contents of the image with 0.
-  void ZeroContents();
+  void set_used_in_replace_contents() { used_in_replace_contents_ = true; }
+
+  // Prepares this image data to be recycled to the plugin. The contents will be
+  // cleared if zero_contents is set.
+  void RecycleToPlugin(bool zero_contents);
 
 #if !defined(OS_NACL)
   static ImageHandle NullHandle();
@@ -84,6 +87,10 @@ class ImageData : public ppapi::Resource,
   scoped_ptr<skia::PlatformCanvas> mapped_canvas_;
 #endif
 
+  // Set to true when this ImageData has been used in a call to
+  // Graphics2D.ReplaceContents. This is used to signal that it can be cached.
+  bool used_in_replace_contents_;
+
   DISALLOW_COPY_AND_ASSIGN(ImageData);
 };