Fix for pinch virtual viewport flag wasn't fully enabled.

content/renderer/gpu/render_widget_compositor.cc

 // Copyright (c) 2013 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 "content/renderer/gpu/render_widget_compositor.h"
 
 #include <limits>
 #include <string>
 
 #if defined(OS_ANDROID)
@@ skipping 169 matching lines @@
 
   if (cmd->HasSwitch(cc::switches::kTopControlsHideThreshold)) {
       std::string top_threshold_str =
           cmd->GetSwitchValueASCII(cc::switches::kTopControlsHideThreshold);
       double hide_threshold;
       if (base::StringToDouble(top_threshold_str, &hide_threshold) &&
           hide_threshold >= 0.f && hide_threshold <= 1.f)
         settings.top_controls_hide_threshold = hide_threshold;
   }
 
+#if defined(OS_CHROMEOS)
+  settings.use_pinch_virtual_viewport = true;
+#else
   settings.use_pinch_virtual_viewport =
       cmd->HasSwitch(cc::switches::kEnablePinchVirtualViewport);
+#endif

[piman, 2014/04/25 20:53:05]

I would prefer if this kind of per-platform decision was in one place, in the
browser, rather than littered all over the code, with different logic - as this
CL shows, it's easy to miss one place and have the wrong behavior.

See for example what we do for IsThreadedCompositingEnabled or
IsDelegatedRendererEnabled or IsImplSidePaintingEnabled etc. in
content/browser/gpu/compositor_util.cc

We have one single place that makes the decision, and then this decision is used
on the browser side, and passed (as a command line flag, for lack of better way)
to the renderer. We can even test that logic.

I think we should be able to easily add a IsPinchVirtualViewportEnabled in
compositor_util.cc, with all the logic there, and use that information to pass a
single enable flag to the renderer (see render_process_host_impl.cc) and use
that flag to make all the decisions.

   settings.allow_antialiasing &=
       !cmd->HasSwitch(cc::switches::kDisableCompositedAntialiasing);
 
   // These flags should be mirrored by UI versions in ui/compositor/.
   settings.initial_debug_state.show_debug_borders =
       cmd->HasSwitch(cc::switches::kShowCompositedLayerBorders);
   settings.initial_debug_state.show_fps_counter =
       cmd->HasSwitch(cc::switches::kShowFPSCounter);
   settings.initial_debug_state.show_layer_animation_bounds_rects =
       cmd->HasSwitch(cc::switches::kShowLayerAnimationBounds);
@@ skipping 80 matching lines @@
     settings.max_memory_for_prepaint_percentage = 50;
   }
   // Webview does not own the surface so should not clear it.
   settings.should_clear_root_render_pass =
       !widget->UsingSynchronousRendererCompositor();
 
 #elif !defined(OS_MACOSX)
   if (ui::IsOverlayScrollbarEnabled()) {
     settings.scrollbar_animator = cc::LayerTreeSettings::Thinning;
     settings.solid_color_scrollbar_color = SkColorSetARGB(128, 128, 128, 128);
-  } else if (cmd->HasSwitch(cc::switches::kEnablePinchVirtualViewport)) {
+  } else if (settings.use_pinch_virtual_viewport) {
     // use_pinch_zoom_scrollbars is only true on desktop when non-overlay
     // scrollbars are in use.
     settings.use_pinch_zoom_scrollbars = true;
     settings.scrollbar_animator = cc::LayerTreeSettings::LinearFade;
     settings.solid_color_scrollbar_color = SkColorSetARGB(128, 128, 128, 128);
   }
 #endif
 
   compositor->Initialize(settings);
 
@@ skipping 348 matching lines @@
   widget_->OnSwapBuffersAborted();
 }
 
 void RenderWidgetCompositor::RateLimitSharedMainThreadContext() {
   cc::ContextProvider* provider =
       RenderThreadImpl::current()->SharedMainThreadContextProvider().get();
   provider->ContextGL()->RateLimitOffscreenContextCHROMIUM();
 }
 
 }  // namespace content