Don't create render passes for transparent images.

cc/damage_tracker_unittest.cc

 // Copyright 2011 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/damage_tracker.h"
 
 #include "cc/layer_impl.h"
 #include "cc/layer_sorter.h"
 #include "cc/layer_tree_host_common.h"
 #include "cc/math_util.h"
@@ skipping 95 matching lines @@
     root->setDrawsContent(true);
     root->createRenderSurface();
     root->renderSurface()->setContentRect(gfx::Rect(gfx::Point(), gfx::Size(500, 500)));
 
     child1->setPosition(gfx::PointF(100, 100));
     child1->setAnchorPoint(gfx::PointF());
     child1->setBounds(gfx::Size(30, 30));
     child1->setContentBounds(gfx::Size(30, 30));
     child1->setOpacity(0.5); // with a child that drawsContent, this will cause the layer to create its own renderSurface.
     child1->setDrawsContent(false); // this layer does not draw, but is intended to create its own renderSurface.
+    child1->setForceRenderSurface(true);
 
     child2->setPosition(gfx::PointF(11, 11));
     child2->setAnchorPoint(gfx::PointF());
     child2->setBounds(gfx::Size(18, 18));
     child2->setContentBounds(gfx::Size(18, 18));
     child2->setDrawsContent(true);
 
     grandChild1->setPosition(gfx::PointF(200, 200));
     grandChild1->setAnchorPoint(gfx::PointF());
     grandChild1->setBounds(gfx::Size(6, 8));
@@ skipping 590 matching lines @@
 {
     scoped_ptr<LayerImpl> root = createAndSetUpTestTreeWithTwoSurfaces();
     LayerImpl* child1 = root->children()[0];
     gfx::RectF childDamageRect;
     gfx::RectF rootDamageRect;
 
     // CASE 1: If a descendant surface disappears, its entire old area becomes exposed.
     //
     clearDamageForAllSurfaces(root.get());
     child1->setOpacity(1);
+    child1->setForceRenderSurface(false);
     emulateDrawingOneFrame(root.get());
 
     // Sanity check that there is only one surface now.
     ASSERT_FALSE(child1->renderSurface());
     ASSERT_EQ(4u, root->renderSurface()->layerList().size());
 
     rootDamageRect = root->renderSurface()->damageTracker()->currentDamageRect();
     EXPECT_FLOAT_RECT_EQ(gfx::RectF(290, 290, 16, 18), rootDamageRect);
 
     // CASE 2: If a descendant surface appears, its entire old area becomes exposed.
 
     // Cycle one frame of no change, just to sanity check that the next rect is not because of the old damage state.
     clearDamageForAllSurfaces(root.get());
     emulateDrawingOneFrame(root.get());
     rootDamageRect = root->renderSurface()->damageTracker()->currentDamageRect();
     EXPECT_TRUE(rootDamageRect.IsEmpty());
 
     // Then change the tree so that the render surface is added back.
     clearDamageForAllSurfaces(root.get());
     child1->setOpacity(0.5);
+    child1->setForceRenderSurface(true);
     emulateDrawingOneFrame(root.get());
 
     // Sanity check that there is a new surface now.
     ASSERT_TRUE(child1->renderSurface());
     EXPECT_EQ(3u, root->renderSurface()->layerList().size());
     EXPECT_EQ(2u, child1->renderSurface()->layerList().size());
 
     childDamageRect = child1->renderSurface()->damageTracker()->currentDamageRect();
     rootDamageRect = root->renderSurface()->damageTracker()->currentDamageRect();
     EXPECT_FLOAT_RECT_EQ(gfx::RectF(190, 190, 16, 18), childDamageRect);
@@ skipping 394 matching lines @@
     EXPECT_TRUE(rootDamageRect.IsEmpty());
 
     // Damage should remain empty even after one frame, since there's yet no new damage
     emulateDrawingOneFrame(root.get());
     rootDamageRect = root->renderSurface()->damageTracker()->currentDamageRect();
     EXPECT_TRUE(rootDamageRect.IsEmpty());
 }
 
 }  // namespace
 }  // namespace cc