Revert 142054 (apparently caused http://crbug.com/132813)

- Make discarding Frontbuffer on mac actually drop resources without a discarded backbuffer.


BUG=132444
TEST=Manual


Review URL: https://chromiumcodereview.appspot.com/10535147

TBR=mmocny@chromium.org
Review URL: https://chromiumcodereview.appspot.com/10580010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@142880 0039d316-1c4b-4281-b951-d872f2087c98

content/common/gpu/image_transport_surface_mac.cc

@@ -52,7 +52,6 @@ class IOSurfaceImageTransportSurface : public gfx::NoOpGLSurfaceCGL,
  private:
   virtual ~IOSurfaceImageTransportSurface() OVERRIDE;
 
-  void AdjustBufferAllocation();
   void UnrefIOSurface();
   void CreateIOSurface();
 
@@ -167,27 +166,22 @@ void IOSurfaceImageTransportSurface::SetBackbufferAllocation(bool allocation) {
   if (backbuffer_suggested_allocation_ == allocation)
     return;
   backbuffer_suggested_allocation_ = allocation;
-  AdjustBufferAllocation();
+
+  if (backbuffer_suggested_allocation_)
+    CreateIOSurface();
+  else
+    UnrefIOSurface();
 }
 
 void IOSurfaceImageTransportSurface::SetFrontbufferAllocation(bool allocation) {
   if (frontbuffer_suggested_allocation_ == allocation)
     return;
   frontbuffer_suggested_allocation_ = allocation;
-  AdjustBufferAllocation();
-}
 
-void IOSurfaceImageTransportSurface::AdjustBufferAllocation() {
-  // On mac, the frontbuffer and backbuffer are the same buffer. The buffer is
-  // free'd when both the browser and gpu processes have Unref'd the IOSurface.
-  if (!backbuffer_suggested_allocation_ &&
-      !frontbuffer_suggested_allocation_ &&
-      io_surface_.get()) {
-    UnrefIOSurface();
+  // We recreate frontbuffer by recreating backbuffer and swapping.
+  // But we release frontbuffer by telling UI to release its handle on it.
+  if (!frontbuffer_suggested_allocation_)
     helper_->Suspend();
-  } else if (backbuffer_suggested_allocation_ && !io_surface_.get()) {
-    CreateIOSurface();
-  }
 }
 
 bool IOSurfaceImageTransportSurface::SwapBuffers() {