Chromium compositor change implementing page-scale driven pinch-zoom.

ui/compositor/compositor.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/compositor/compositor.h"
 
 #include <algorithm>
 
 #include "base/command_line.h"
 #include "base/threading/thread_restrictions.h"
@@ skipping 168 matching lines @@
 
 void Compositor::Initialize(bool use_thread) {
   CommandLine* command_line = CommandLine::ForCurrentProcess();
   WebKit::WebCompositorSupport* compositor_support =
       WebKit::Platform::current()->compositorSupport();
   // These settings must be applied before we initialize the compositor.
   compositor_support->setPartialSwapEnabled(
       command_line->HasSwitch(switches::kUIEnablePartialSwap));
   compositor_support->setPerTilePaintingEnabled(
       command_line->HasSwitch(switches::kUIEnablePerTilePainting));
+  compositor_support->setPageScalePinchZoomEnabled(
+      command_line->HasSwitch(switches::kEnablePinchInCompositor));

[piman, 2012/10/05 00:01:08]

Do we really want to pinch-zoom the UI?

[Jeff Timanus, 2012/10/05 00:05:34]

I'm not sure if I understand your question.  This particular call pushes the
switch state for the new flag to the compositor, which is used to selectively
enable my new pinch patch.

As I understand the implementation, the browser UI should never be scaled, only
the contents of the root scroll layer.

[piman, 2012/10/05 00:25:51]

This is the UI's compositor. Why are we doing anything to it?

[Jeff Timanus, 2012/10/05 15:37:50]

Ah.  It's possible that I did not understand the different compositor
environments.  I followed the existing flag behaviour to push the pinch state to
the compositor.

I don't think pinch should be relevant for the UI.  If I remove this call, and
rely on the similar path in content/renderer/render_thread_impl.cc, should that
suffice for only modifying the settings state of the web-contents compositor?

   if (use_thread)
     g_compositor_thread = new webkit_glue::WebThreadImpl("Browser Compositor");
   compositor_support->initialize(g_compositor_thread);
 }
 
 void Compositor::Terminate() {
   WebKit::Platform::current()->compositorSupport()->shutdown();
   if (g_compositor_thread) {
     delete g_compositor_thread;
     g_compositor_thread = NULL;
@@ skipping 239 matching lines @@
 
 COMPOSITOR_EXPORT void DisableTestCompositor() {
   test_compositor_enabled = false;
 }
 
 COMPOSITOR_EXPORT bool IsTestCompositorEnabled() {
   return test_compositor_enabled;
 }
 
 }  // namespace ui