cc: Fix PostiveRatio crash by checking raster scale

cc/picture_layer_impl.cc

 // Copyright 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 "cc/picture_layer_impl.h"
 
 #include "base/time.h"
 #include "cc/append_quads_data.h"
 #include "cc/checkerboard_draw_quad.h"
 #include "cc/debug_border_draw_quad.h"
@@ skipping 552 matching lines @@
   // a throttled rate. Possibly make use of invalidation_.IsEmpty() on pending
   // tree. This will allow CSS scale changes to get re-rastered at an
   // appropriate rate.
 
   if (is_active_layer) {
     if (raster_source_scale_was_animating_ && !animating_transform_to_screen)
       change_target_tiling = true;
     raster_source_scale_was_animating_ = animating_transform_to_screen;
   }
 
-  if (is_active_layer && is_pinching) {
+  if (is_active_layer && is_pinching && raster_page_scale_) {

[danakj, 2013/02/11 23:11:35]

I guess all of these if()s could be guarded by (...&& !change_target_tiling) to
deal with this, and ensure only the last positive case happens.

But I guess this way is also more ordering-independent for better or worse.

[enne (OOO), 2013/02/12 02:18:20]

Or put it all in a helper function? Anyway, I'm just trying to fix this crash
for now, so am going to land this as-is.

     // If the page scale diverges too far during pinch, change raster target to
     // the current page scale.
     float ratio = PositiveRatio(ideal_page_scale_, raster_page_scale_);
     if (ratio >= kMaxScaleRatioDuringPinch)
       change_target_tiling = true;
   }
 
   if (!is_pinching) {
     // When not pinching, match the ideal page scale factor.
     if (raster_page_scale_ != ideal_page_scale_)
@@ skipping 129 matching lines @@
   return twin;
 }
 
 void PictureLayerImpl::getDebugBorderProperties(
     SkColor* color, float* width) const {
   *color = DebugColors::TiledContentLayerBorderColor();
   *width = DebugColors::TiledContentLayerBorderWidth(layerTreeImpl());
 }
 
 }  // namespace cc