Pinch/Zoom Infrastructure & Plumbing CL

This CL supplies the necessary changes to CC to support the
inner/outer viewport model for pinch-zoom and fixed-position 
elements. The specification for these changes is contained in 
the document "Layer-based Solution for Pinch Zoom / Fixed 
Position".

It incorporates a change to how scrollbar parameters are 
computed (removes the notion of max_scroll_offset as a 
quantity set be the embedder, and instead inferred from the 
relative sizes of a clip layer w.r.t. the scroll layer).

Scrollbars are generalized so that a layer may have more than 
two scrollbars, and the parameters of the scrollbar are set 
w.r.t. the sizes and positions of a clip and a scroll layer. 
Further, changes to the scrip/scroll layer automatically 
notify any attached scrollbars.

The CL also removes existing references to root_scroll_layer 
from LTH, LTI and LTHI and replaces them with either 
Inner/OuterViewportScrollLayer (dual-layer operation only 
exists at present if the --enable-pinch-virtual-viewport flag 
is specified, otherwise behavior is unchanged).

Logic is added to (i) combine scroll offsets for the two 
viewports before passing it to the embedder, and (ii) 
splitting any offsets received from the embedder 
appropriately between the two viewports.

This CL relies on https://codereview.chromium.org/138453004/ 
for changes in Blink to support it.

BUG=148816

Review URL: https://codereview.chromium.org/23983047

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246812 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 213 insertions, 109 deletions

diff --git a/cc/trees/layer_tree_host_unittest_scroll.cc b/cc/trees/layer_tree_host_unittest_scroll.cc
index 3871154..c7ea722 100644
--- a/cc/trees/layer_tree_host_unittest_scroll.cc
+++ b/cc/trees/layer_tree_host_unittest_scroll.cc
@@ -31,42 +31,53 @@ class LayerTreeHostScrollTestScrollSimple : public LayerTreeHostScrollTest {
         num_scrolls_(0) {}
 
   virtual void BeginTest() OVERRIDE {
-    layer_tree_host()->root_layer()->SetScrollable(true);
-    layer_tree_host()->root_layer()
-        ->SetMaxScrollOffset(gfx::Vector2d(100, 100));
-    layer_tree_host()->root_layer()->SetScrollOffset(initial_scroll_);
+    Layer* root_layer = layer_tree_host()->root_layer();
+    scoped_refptr<Layer> scroll_layer = Layer::Create();
+    root_layer->AddChild(scroll_layer);
+    // Create an effective max_scroll_offset of (100, 100).
+    scroll_layer->SetBounds(gfx::Size(root_layer->bounds().width() + 100,
+                                      root_layer->bounds().height() + 100));
+    scroll_layer->SetIsDrawable(true);
+    scroll_layer->SetIsContainerForFixedPositionLayers(true);
+    scroll_layer->SetScrollClipLayer(root_layer);
+    scroll_layer->SetScrollOffset(initial_scroll_);
+    layer_tree_host()->RegisterViewportLayers(root_layer, scroll_layer, NULL);
     PostSetNeedsCommitToMainThread();
   }
 
   virtual void Layout() OVERRIDE {
     Layer* root = layer_tree_host()->root_layer();
+    Layer* scroll_layer = root->children()[0];
     if (!layer_tree_host()->source_frame_number()) {
-      EXPECT_VECTOR_EQ(initial_scroll_, root->scroll_offset());
+      EXPECT_VECTOR_EQ(initial_scroll_, scroll_layer->scroll_offset());
     } else {
-      EXPECT_VECTOR_EQ(initial_scroll_ + scroll_amount_, root->scroll_offset());
+      EXPECT_VECTOR_EQ(initial_scroll_ + scroll_amount_,
+                       scroll_layer->scroll_offset());
 
       // Pretend like Javascript updated the scroll position itself.
-      root->SetScrollOffset(second_scroll_);
+      scroll_layer->SetScrollOffset(second_scroll_);
     }
   }
 
   virtual void DrawLayersOnThread(LayerTreeHostImpl* impl) OVERRIDE {
     LayerImpl* root = impl->active_tree()->root_layer();
-    EXPECT_VECTOR_EQ(gfx::Vector2d(), root->ScrollDelta());
+    LayerImpl* scroll_layer = root->children()[0];
+    EXPECT_VECTOR_EQ(gfx::Vector2d(), scroll_layer->ScrollDelta());
 
-    root->SetScrollable(true);
-    root->SetMaxScrollOffset(gfx::Vector2d(100, 100));
-    root->ScrollBy(scroll_amount_);
+    scroll_layer->SetScrollClipLayer(root->id());
+    scroll_layer->SetBounds(
+        gfx::Size(root->bounds().width() + 100, root->bounds().height() + 100));
+    scroll_layer->ScrollBy(scroll_amount_);
 
     switch (impl->active_tree()->source_frame_number()) {
       case 0:
-        EXPECT_VECTOR_EQ(initial_scroll_, root->scroll_offset());
-        EXPECT_VECTOR_EQ(scroll_amount_, root->ScrollDelta());
+        EXPECT_VECTOR_EQ(initial_scroll_, scroll_layer->scroll_offset());
+        EXPECT_VECTOR_EQ(scroll_amount_, scroll_layer->ScrollDelta());
         PostSetNeedsCommitToMainThread();
         break;
       case 1:
-        EXPECT_VECTOR_EQ(root->scroll_offset(), second_scroll_);
-        EXPECT_VECTOR_EQ(root->ScrollDelta(), scroll_amount_);
+        EXPECT_VECTOR_EQ(scroll_layer->scroll_offset(), second_scroll_);
+        EXPECT_VECTOR_EQ(scroll_layer->ScrollDelta(), scroll_amount_);
         EndTest();
         break;
     }
@@ -95,55 +106,62 @@ class LayerTreeHostScrollTestScrollMultipleRedraw
       : initial_scroll_(40, 10), scroll_amount_(-3, 17), num_scrolls_(0) {}
 
   virtual void BeginTest() OVERRIDE {
-    layer_tree_host()->root_layer()->SetScrollable(true);
-    layer_tree_host()->root_layer()->SetScrollOffset(initial_scroll_);
-    layer_tree_host()->root_layer()->SetBounds(gfx::Size(200, 200));
-    layer_tree_host()->root_layer()
-        ->SetMaxScrollOffset(gfx::Vector2d(100, 100));
+    Layer* root_layer = layer_tree_host()->root_layer();
+    scroll_layer_ = Layer::Create();
+    root_layer->AddChild(scroll_layer_);
+    // Create an effective max_scroll_offset of (100, 100).
+    scroll_layer_->SetBounds(gfx::Size(root_layer->bounds().width() + 100,
+                                       root_layer->bounds().height() + 100));
+    scroll_layer_->SetIsDrawable(true);
+    scroll_layer_->SetIsContainerForFixedPositionLayers(true);
+    scroll_layer_->SetScrollClipLayer(root_layer);
+    scroll_layer_->SetScrollOffset(initial_scroll_);
+    layer_tree_host()->RegisterViewportLayers(root_layer, scroll_layer_, NULL);
     PostSetNeedsCommitToMainThread();
   }
 
   virtual void BeginCommitOnThread(LayerTreeHostImpl* impl) OVERRIDE {
-    Layer* root = layer_tree_host()->root_layer();
     switch (layer_tree_host()->source_frame_number()) {
       case 0:
-        EXPECT_VECTOR_EQ(root->scroll_offset(), initial_scroll_);
+        EXPECT_VECTOR_EQ(scroll_layer_->scroll_offset(), initial_scroll_);
         break;
       case 1:
-        EXPECT_VECTOR_EQ(root->scroll_offset(),
+        EXPECT_VECTOR_EQ(scroll_layer_->scroll_offset(),
                          initial_scroll_ + scroll_amount_ + scroll_amount_);
       case 2:
-        EXPECT_VECTOR_EQ(root->scroll_offset(),
+        EXPECT_VECTOR_EQ(scroll_layer_->scroll_offset(),
                          initial_scroll_ + scroll_amount_ + scroll_amount_);
         break;
     }
   }
 
   virtual void DrawLayersOnThread(LayerTreeHostImpl* impl) OVERRIDE {
-    LayerImpl* root = impl->active_tree()->root_layer();
+    LayerImpl* scroll_layer =
+        impl->active_tree()->LayerById(scroll_layer_->id());
     if (impl->active_tree()->source_frame_number() == 0 &&
         impl->SourceAnimationFrameNumber() == 1) {
       // First draw after first commit.
-      EXPECT_VECTOR_EQ(root->ScrollDelta(), gfx::Vector2d());
-      root->ScrollBy(scroll_amount_);
-      EXPECT_VECTOR_EQ(root->ScrollDelta(), scroll_amount_);
+      EXPECT_VECTOR_EQ(scroll_layer->ScrollDelta(), gfx::Vector2d());
+      scroll_layer->ScrollBy(scroll_amount_);
+      EXPECT_VECTOR_EQ(scroll_layer->ScrollDelta(), scroll_amount_);
 
-      EXPECT_VECTOR_EQ(root->scroll_offset(), initial_scroll_);
+      EXPECT_VECTOR_EQ(scroll_layer->scroll_offset(), initial_scroll_);
       PostSetNeedsRedrawToMainThread();
     } else if (impl->active_tree()->source_frame_number() == 0 &&
                impl->SourceAnimationFrameNumber() == 2) {
       // Second draw after first commit.
-      EXPECT_EQ(root->ScrollDelta(), scroll_amount_);
-      root->ScrollBy(scroll_amount_);
-      EXPECT_VECTOR_EQ(root->ScrollDelta(), scroll_amount_ + scroll_amount_);
+      EXPECT_EQ(scroll_layer->ScrollDelta(), scroll_amount_);
+      scroll_layer->ScrollBy(scroll_amount_);
+      EXPECT_VECTOR_EQ(scroll_layer->ScrollDelta(),
+                       scroll_amount_ + scroll_amount_);
 
-      EXPECT_VECTOR_EQ(root->scroll_offset(), initial_scroll_);
+      EXPECT_VECTOR_EQ(scroll_layer_->scroll_offset(), initial_scroll_);
       PostSetNeedsCommitToMainThread();
     } else if (impl->active_tree()->source_frame_number() == 1) {
       // Third or later draw after second commit.
       EXPECT_GE(impl->SourceAnimationFrameNumber(), 3);
-      EXPECT_VECTOR_EQ(root->ScrollDelta(), gfx::Vector2d());
-      EXPECT_VECTOR_EQ(root->scroll_offset(),
+      EXPECT_VECTOR_EQ(scroll_layer_->ScrollDelta(), gfx::Vector2d());
+      EXPECT_VECTOR_EQ(scroll_layer_->scroll_offset(),
                        initial_scroll_ + scroll_amount_ + scroll_amount_);
       EndTest();
     }
@@ -160,6 +178,7 @@ class LayerTreeHostScrollTestScrollMultipleRedraw
   gfx::Vector2d initial_scroll_;
   gfx::Vector2d scroll_amount_;
   int num_scrolls_;
+  scoped_refptr<Layer> scroll_layer_;
 };
 
 MULTI_THREAD_TEST_F(LayerTreeHostScrollTestScrollMultipleRedraw);
@@ -183,14 +202,17 @@ class LayerTreeHostScrollTestScrollAbortedCommit
 
   virtual void SetupTree() OVERRIDE {
     LayerTreeHostScrollTest::SetupTree();
+    Layer* root_layer = layer_tree_host()->root_layer();
     scoped_refptr<Layer> root_scroll_layer = Layer::Create();
-    root_scroll_layer->SetScrollable(true);
+    root_scroll_layer->SetScrollClipLayer(root_layer);
     root_scroll_layer->SetScrollOffset(initial_scroll_);
     root_scroll_layer->SetBounds(gfx::Size(200, 200));
-    root_scroll_layer->SetMaxScrollOffset(gfx::Vector2d(100, 100));
     root_scroll_layer->SetIsDrawable(true);
-    layer_tree_host()->root_layer()->AddChild(root_scroll_layer);
+    root_scroll_layer->SetIsContainerForFixedPositionLayers(true);
+    root_layer->AddChild(root_scroll_layer);
 
+    layer_tree_host()->RegisterViewportLayers(
+        root_layer, root_scroll_layer, NULL);
     layer_tree_host()->SetPageScaleFactorAndLimits(1.f, 0.01f, 100.f);
   }
 
@@ -344,42 +366,57 @@ class LayerTreeHostScrollTestFractionalScroll : public LayerTreeHostScrollTest {
  public:
   LayerTreeHostScrollTestFractionalScroll() : scroll_amount_(1.75, 0) {}
 
+  virtual void SetupTree() OVERRIDE {
+    LayerTreeHostScrollTest::SetupTree();
+    Layer* root_layer = layer_tree_host()->root_layer();
+    scoped_refptr<Layer> root_scroll_layer = Layer::Create();
+    root_scroll_layer->SetScrollClipLayer(root_layer);
+    root_scroll_layer->SetBounds(
+        gfx::Size(root_layer->bounds().width() + 100,
+                  root_layer->bounds().height() + 100));
+    root_scroll_layer->SetIsDrawable(true);
+    root_scroll_layer->SetIsContainerForFixedPositionLayers(true);
+    root_layer->AddChild(root_scroll_layer);
+
+    layer_tree_host()->RegisterViewportLayers(
+        root_layer, root_scroll_layer, NULL);
+    layer_tree_host()->SetPageScaleFactorAndLimits(1.f, 0.01f, 100.f);
+  }
+
   virtual void BeginTest() OVERRIDE {
-    layer_tree_host()->root_layer()->SetScrollable(true);
-    layer_tree_host()->root_layer()
-        ->SetMaxScrollOffset(gfx::Vector2d(100, 100));
     PostSetNeedsCommitToMainThread();
   }
 
   virtual void DrawLayersOnThread(LayerTreeHostImpl* impl) OVERRIDE {
     LayerImpl* root = impl->active_tree()->root_layer();
+    LayerImpl* scroll_layer = root->children()[0];
 
     // Check that a fractional scroll delta is correctly accumulated over
     // multiple commits.
     switch (impl->active_tree()->source_frame_number()) {
       case 0:
-        EXPECT_VECTOR_EQ(root->scroll_offset(), gfx::Vector2d(0, 0));
-        EXPECT_VECTOR_EQ(root->ScrollDelta(), gfx::Vector2d(0, 0));
+        EXPECT_VECTOR_EQ(scroll_layer->scroll_offset(), gfx::Vector2d(0, 0));
+        EXPECT_VECTOR_EQ(scroll_layer->ScrollDelta(), gfx::Vector2d(0, 0));
         PostSetNeedsCommitToMainThread();
         break;
       case 1:
-        EXPECT_VECTOR_EQ(root->scroll_offset(),
+        EXPECT_VECTOR_EQ(scroll_layer->scroll_offset(),
                          gfx::ToFlooredVector2d(scroll_amount_));
-        EXPECT_VECTOR_EQ(root->ScrollDelta(),
+        EXPECT_VECTOR_EQ(scroll_layer->ScrollDelta(),
                          gfx::Vector2dF(fmod(scroll_amount_.x(), 1.0f), 0.0f));
         PostSetNeedsCommitToMainThread();
         break;
       case 2:
         EXPECT_VECTOR_EQ(
-            root->scroll_offset(),
+            scroll_layer->scroll_offset(),
             gfx::ToFlooredVector2d(scroll_amount_ + scroll_amount_));
         EXPECT_VECTOR_EQ(
-            root->ScrollDelta(),
+            scroll_layer->ScrollDelta(),
             gfx::Vector2dF(fmod(2.0f * scroll_amount_.x(), 1.0f), 0.0f));
         EndTest();
         break;
     }
-    root->ScrollBy(scroll_amount_);
+    scroll_layer->ScrollBy(scroll_amount_);
   }
 
   virtual void AfterTest() OVERRIDE {}
@@ -411,8 +448,8 @@ class LayerTreeHostScrollTestCaseWithChild : public LayerTreeHostScrollTest {
     root_scroll_layer_->SetAnchorPoint(gfx::PointF());
 
     root_scroll_layer_->SetIsDrawable(true);
-    root_scroll_layer_->SetScrollable(true);
-    root_scroll_layer_->SetMaxScrollOffset(gfx::Vector2d(100, 100));
+    root_scroll_layer_->SetScrollClipLayer(root_layer);
+    root_scroll_layer_->SetIsContainerForFixedPositionLayers(true);
     root_layer->AddChild(root_scroll_layer_);
 
     child_layer_ = ContentLayer::Create(&fake_content_layer_client_);
@@ -433,8 +470,8 @@ class LayerTreeHostScrollTestCaseWithChild : public LayerTreeHostScrollTest {
     child_layer_->SetAnchorPoint(gfx::PointF());
 
     child_layer_->SetIsDrawable(true);
-    child_layer_->SetScrollable(true);
-    child_layer_->SetMaxScrollOffset(gfx::Vector2d(100, 100));
+    child_layer_->SetScrollClipLayer(root_layer);
+    child_layer_->SetBounds(root_scroll_layer_->bounds());
     root_scroll_layer_->AddChild(child_layer_);
 
     if (scroll_child_layer_) {
@@ -448,6 +485,8 @@ class LayerTreeHostScrollTestCaseWithChild : public LayerTreeHostScrollTest {
     expected_scroll_layer_->SetScrollOffset(initial_offset_);
 
     layer_tree_host()->SetRootLayer(root_layer);
+    layer_tree_host()->RegisterViewportLayers(
+        root_layer, root_scroll_layer_, NULL);
     LayerTreeHostScrollTest::SetupTree();
   }
 
@@ -724,26 +763,41 @@ class ImplSidePaintingScrollTestSimple : public ImplSidePaintingScrollTest {
         impl_thread_scroll2_(-3, 10),
         num_scrolls_(0) {}
 
+  virtual void SetupTree() OVERRIDE {
+    LayerTreeHostScrollTest::SetupTree();
+    Layer* root_layer = layer_tree_host()->root_layer();
+    scoped_refptr<Layer> root_scroll_layer = Layer::Create();
+    root_scroll_layer->SetScrollClipLayer(root_layer);
+    root_scroll_layer->SetScrollOffset(initial_scroll_);
+    root_scroll_layer->SetBounds(
+        gfx::Size(root_layer->bounds().width() + 100,
+                  root_layer->bounds().height() + 100));
+    root_scroll_layer->SetIsDrawable(true);
+    root_scroll_layer->SetIsContainerForFixedPositionLayers(true);
+    root_layer->AddChild(root_scroll_layer);
+
+    layer_tree_host()->RegisterViewportLayers(
+        root_layer, root_scroll_layer, NULL);
+    layer_tree_host()->SetPageScaleFactorAndLimits(1.f, 0.01f, 100.f);
+  }
+
   virtual void BeginTest() OVERRIDE {
-    layer_tree_host()->root_layer()->SetScrollable(true);
-    layer_tree_host()->root_layer()
-        ->SetMaxScrollOffset(gfx::Vector2d(100, 100));
-    layer_tree_host()->root_layer()->SetScrollOffset(initial_scroll_);
     PostSetNeedsCommitToMainThread();
   }
 
   virtual void Layout() OVERRIDE {
     Layer* root = layer_tree_host()->root_layer();
+    Layer* scroll_layer = root->children()[0];
     if (!layer_tree_host()->source_frame_number()) {
-      EXPECT_VECTOR_EQ(root->scroll_offset(), initial_scroll_);
+      EXPECT_VECTOR_EQ(scroll_layer->scroll_offset(), initial_scroll_);
     } else {
-      EXPECT_VECTOR_EQ(root->scroll_offset(),
+      EXPECT_VECTOR_EQ(scroll_layer->scroll_offset(),
                        initial_scroll_ + impl_thread_scroll1_);
 
       // Pretend like Javascript updated the scroll position itself with a
       // change of main_thread_scroll.
-      root->SetScrollOffset(initial_scroll_ + main_thread_scroll_ +
-                            impl_thread_scroll1_);
+      scroll_layer->SetScrollOffset(initial_scroll_ + main_thread_scroll_ +
+                                    impl_thread_scroll1_);
     }
   }
 
@@ -758,6 +812,7 @@ class ImplSidePaintingScrollTestSimple : public ImplSidePaintingScrollTest {
     ImplSidePaintingScrollTest::DrawLayersOnThread(impl);
 
     LayerImpl* root = impl->active_tree()->root_layer();
+    LayerImpl* scroll_layer = root->children()[0];
     LayerImpl* pending_root =
         impl->active_tree()->FindPendingTreeLayerById(root->id());
 
@@ -765,12 +820,12 @@ class ImplSidePaintingScrollTestSimple : public ImplSidePaintingScrollTest {
       case 0:
         if (!impl->pending_tree()) {
           impl->BlockNotifyReadyToActivateForTesting(true);
-          EXPECT_VECTOR_EQ(root->ScrollDelta(), gfx::Vector2d());
-          root->ScrollBy(impl_thread_scroll1_);
+          EXPECT_VECTOR_EQ(scroll_layer->ScrollDelta(), gfx::Vector2d());
+          scroll_layer->ScrollBy(impl_thread_scroll1_);
 
-          EXPECT_VECTOR_EQ(root->scroll_offset(), initial_scroll_);
-          EXPECT_VECTOR_EQ(root->ScrollDelta(), impl_thread_scroll1_);
-          EXPECT_VECTOR_EQ(root->sent_scroll_delta(), gfx::Vector2d());
+          EXPECT_VECTOR_EQ(scroll_layer->scroll_offset(), initial_scroll_);
+          EXPECT_VECTOR_EQ(scroll_layer->ScrollDelta(), impl_thread_scroll1_);
+          EXPECT_VECTOR_EQ(scroll_layer->sent_scroll_delta(), gfx::Vector2d());
           PostSetNeedsCommitToMainThread();
 
           // CommitCompleteOnThread will trigger this function again
@@ -780,26 +835,30 @@ class ImplSidePaintingScrollTestSimple : public ImplSidePaintingScrollTest {
           ASSERT_TRUE(pending_root);
           EXPECT_EQ(impl->pending_tree()->source_frame_number(), 1);
 
-          root->ScrollBy(impl_thread_scroll2_);
-          EXPECT_VECTOR_EQ(root->scroll_offset(), initial_scroll_);
-          EXPECT_VECTOR_EQ(root->ScrollDelta(),
+          scroll_layer->ScrollBy(impl_thread_scroll2_);
+          EXPECT_VECTOR_EQ(scroll_layer->scroll_offset(), initial_scroll_);
+          EXPECT_VECTOR_EQ(scroll_layer->ScrollDelta(),
                            impl_thread_scroll1_ + impl_thread_scroll2_);
-          EXPECT_VECTOR_EQ(root->sent_scroll_delta(), impl_thread_scroll1_);
+          EXPECT_VECTOR_EQ(scroll_layer->sent_scroll_delta(),
+                           impl_thread_scroll1_);
 
+          LayerImpl* pending_scroll_layer = pending_root->children()[0];
           EXPECT_VECTOR_EQ(
-              pending_root->scroll_offset(),
+              pending_scroll_layer->scroll_offset(),
               initial_scroll_ + main_thread_scroll_ + impl_thread_scroll1_);
-          EXPECT_VECTOR_EQ(pending_root->ScrollDelta(), impl_thread_scroll2_);
-          EXPECT_VECTOR_EQ(pending_root->sent_scroll_delta(), gfx::Vector2d());
+          EXPECT_VECTOR_EQ(pending_scroll_layer->ScrollDelta(),
+                           impl_thread_scroll2_);
+          EXPECT_VECTOR_EQ(pending_scroll_layer->sent_scroll_delta(),
+                           gfx::Vector2d());
         }
         break;
       case 1:
         EXPECT_FALSE(impl->pending_tree());
         EXPECT_VECTOR_EQ(
-            root->scroll_offset(),
+            scroll_layer->scroll_offset(),
             initial_scroll_ + main_thread_scroll_ + impl_thread_scroll1_);
-        EXPECT_VECTOR_EQ(root->ScrollDelta(), impl_thread_scroll2_);
-        EXPECT_VECTOR_EQ(root->sent_scroll_delta(), gfx::Vector2d());
+        EXPECT_VECTOR_EQ(scroll_layer->ScrollDelta(), impl_thread_scroll2_);
+        EXPECT_VECTOR_EQ(scroll_layer->sent_scroll_delta(), gfx::Vector2d());
         EndTest();
         break;
     }
@@ -832,25 +891,40 @@ class ImplSidePaintingScrollTestImplOnlyScroll
   ImplSidePaintingScrollTestImplOnlyScroll()
       : initial_scroll_(20, 10), impl_thread_scroll_(-2, 3) {}
 
+  virtual void SetupTree() OVERRIDE {
+    LayerTreeHostScrollTest::SetupTree();
+    Layer* root_layer = layer_tree_host()->root_layer();
+    scoped_refptr<Layer> root_scroll_layer = Layer::Create();
+    root_scroll_layer->SetScrollClipLayer(root_layer);
+    root_scroll_layer->SetScrollOffset(initial_scroll_);
+    root_scroll_layer->SetBounds(
+        gfx::Size(root_layer->bounds().width() + 100,
+                  root_layer->bounds().height() + 100));
+    root_scroll_layer->SetIsDrawable(true);
+    root_scroll_layer->SetIsContainerForFixedPositionLayers(true);
+    root_layer->AddChild(root_scroll_layer);
+
+    layer_tree_host()->RegisterViewportLayers(
+        root_layer, root_scroll_layer, NULL);
+    layer_tree_host()->SetPageScaleFactorAndLimits(1.f, 0.01f, 100.f);
+  }
+
   virtual void BeginTest() OVERRIDE {
-    layer_tree_host()->root_layer()->SetScrollable(true);
-    layer_tree_host()->root_layer()->SetMaxScrollOffset(
-        gfx::Vector2d(100, 100));
-    layer_tree_host()->root_layer()->SetScrollOffset(initial_scroll_);
     PostSetNeedsCommitToMainThread();
   }
 
   virtual void WillCommit() OVERRIDE {
     Layer* root = layer_tree_host()->root_layer();
+    Layer* scroll_layer = root->children()[0];
     switch (layer_tree_host()->source_frame_number()) {
       case 0:
-        EXPECT_TRUE(root->needs_push_properties());
+        EXPECT_TRUE(scroll_layer->needs_push_properties());
         break;
       case 1:
         // Even if this layer doesn't need push properties, it should
         // still pick up scrolls that happen on the active layer during
         // commit.
-        EXPECT_FALSE(root->needs_push_properties());
+        EXPECT_FALSE(scroll_layer->needs_push_properties());
         break;
     }
   }
@@ -859,8 +933,10 @@ class ImplSidePaintingScrollTestImplOnlyScroll
     // Scroll after the 2nd commit has started.
     if (impl->active_tree()->source_frame_number() == 0) {
       LayerImpl* active_root = impl->active_tree()->root_layer();
+      LayerImpl* active_scroll_layer = active_root->children()[0];
       ASSERT_TRUE(active_root);
-      active_root->ScrollBy(impl_thread_scroll_);
+      ASSERT_TRUE(active_scroll_layer);
+      active_scroll_layer->ScrollBy(impl_thread_scroll_);
     }
   }
 
@@ -868,33 +944,45 @@ class ImplSidePaintingScrollTestImplOnlyScroll
     // We force a second draw here of the first commit before activating
     // the second commit.
     LayerImpl* active_root = impl->active_tree()->root_layer();
+    LayerImpl* active_scroll_layer =
+        active_root ? active_root->children()[0] : NULL;
     LayerImpl* pending_root = impl->pending_tree()->root_layer();
+    LayerImpl* pending_scroll_layer = pending_root->children()[0];
 
     ASSERT_TRUE(pending_root);
+    ASSERT_TRUE(pending_scroll_layer);
     switch (impl->pending_tree()->source_frame_number()) {
       case 0:
-        EXPECT_VECTOR_EQ(pending_root->scroll_offset(), initial_scroll_);
-        EXPECT_VECTOR_EQ(pending_root->ScrollDelta(), gfx::Vector2d());
-        EXPECT_VECTOR_EQ(pending_root->sent_scroll_delta(), gfx::Vector2d());
+        EXPECT_VECTOR_EQ(pending_scroll_layer->scroll_offset(),
+                         initial_scroll_);
+        EXPECT_VECTOR_EQ(pending_scroll_layer->ScrollDelta(), gfx::Vector2d());
+        EXPECT_VECTOR_EQ(pending_scroll_layer->sent_scroll_delta(),
+                         gfx::Vector2d());
         EXPECT_FALSE(active_root);
         break;
       case 1:
         // Even though the scroll happened during the commit, both layers
         // should have the appropriate scroll delta.
-        EXPECT_VECTOR_EQ(pending_root->scroll_offset(), initial_scroll_);
-        EXPECT_VECTOR_EQ(pending_root->ScrollDelta(), impl_thread_scroll_);
-        EXPECT_VECTOR_EQ(pending_root->sent_scroll_delta(), gfx::Vector2d());
+        EXPECT_VECTOR_EQ(pending_scroll_layer->scroll_offset(),
+                         initial_scroll_);
+        EXPECT_VECTOR_EQ(pending_scroll_layer->ScrollDelta(),
+                         impl_thread_scroll_);
+        EXPECT_VECTOR_EQ(pending_scroll_layer->sent_scroll_delta(),
+                         gfx::Vector2d());
         ASSERT_TRUE(active_root);
-        EXPECT_VECTOR_EQ(active_root->scroll_offset(), initial_scroll_);
-        EXPECT_VECTOR_EQ(active_root->ScrollDelta(), impl_thread_scroll_);
-        EXPECT_VECTOR_EQ(active_root->sent_scroll_delta(), gfx::Vector2d());
+        EXPECT_VECTOR_EQ(active_scroll_layer->scroll_offset(), initial_scroll_);
+        EXPECT_VECTOR_EQ(active_scroll_layer->ScrollDelta(),
+                         impl_thread_scroll_);
+        EXPECT_VECTOR_EQ(active_scroll_layer->sent_scroll_delta(),
+                         gfx::Vector2d());
         break;
       case 2:
         // On the next commit, this delta should have been sent and applied.
-        EXPECT_VECTOR_EQ(pending_root->scroll_offset(),
+        EXPECT_VECTOR_EQ(pending_scroll_layer->scroll_offset(),
                          initial_scroll_ + impl_thread_scroll_);
-        EXPECT_VECTOR_EQ(pending_root->ScrollDelta(), gfx::Vector2d());
-        EXPECT_VECTOR_EQ(pending_root->sent_scroll_delta(), gfx::Vector2d());
+        EXPECT_VECTOR_EQ(pending_scroll_layer->ScrollDelta(), gfx::Vector2d());
+        EXPECT_VECTOR_EQ(pending_scroll_layer->sent_scroll_delta(),
+                         gfx::Vector2d());
         EndTest();
         break;
     }
@@ -904,18 +992,19 @@ class ImplSidePaintingScrollTestImplOnlyScroll
     ImplSidePaintingScrollTest::DrawLayersOnThread(impl);
 
     LayerImpl* root = impl->active_tree()->root_layer();
+    LayerImpl* scroll_layer = root->children()[0];
 
     switch (impl->active_tree()->source_frame_number()) {
       case 0:
-        EXPECT_VECTOR_EQ(root->scroll_offset(), initial_scroll_);
-        EXPECT_VECTOR_EQ(root->ScrollDelta(), gfx::Vector2d());
-        EXPECT_VECTOR_EQ(root->sent_scroll_delta(), gfx::Vector2d());
+        EXPECT_VECTOR_EQ(scroll_layer->scroll_offset(), initial_scroll_);
+        EXPECT_VECTOR_EQ(scroll_layer->ScrollDelta(), gfx::Vector2d());
+        EXPECT_VECTOR_EQ(scroll_layer->sent_scroll_delta(), gfx::Vector2d());
         PostSetNeedsCommitToMainThread();
         break;
       case 1:
-        EXPECT_VECTOR_EQ(root->scroll_offset(), initial_scroll_);
-        EXPECT_VECTOR_EQ(root->ScrollDelta(), impl_thread_scroll_);
-        EXPECT_VECTOR_EQ(root->sent_scroll_delta(), gfx::Vector2d());
+        EXPECT_VECTOR_EQ(scroll_layer->scroll_offset(), initial_scroll_);
+        EXPECT_VECTOR_EQ(scroll_layer->ScrollDelta(), impl_thread_scroll_);
+        EXPECT_VECTOR_EQ(scroll_layer->sent_scroll_delta(), gfx::Vector2d());
         PostSetNeedsCommitToMainThread();
         break;
     }
@@ -935,23 +1024,37 @@ class LayerTreeHostScrollTestScrollZeroMaxScrollOffset
  public:
   LayerTreeHostScrollTestScrollZeroMaxScrollOffset() {}
 
+  virtual void SetupTree() OVERRIDE {
+    LayerTreeTest::SetupTree();
+    scoped_refptr<Layer> scroll_layer = Layer::Create();
+    layer_tree_host()->root_layer()->AddChild(scroll_layer);
+  }
+
   virtual void BeginTest() OVERRIDE { PostSetNeedsCommitToMainThread(); }
 
   virtual void DrawLayersOnThread(LayerTreeHostImpl* impl) OVERRIDE {
     LayerImpl* root = impl->active_tree()->root_layer();
-    root->SetScrollable(true);
+    LayerImpl* scroll_layer = root->children()[0];
+    scroll_layer->SetScrollClipLayer(root->id());
 
-    root->SetMaxScrollOffset(gfx::Vector2d(100, 100));
+    // Set max_scroll_offset = (100, 100).
+    scroll_layer->SetBounds(
+        gfx::Size(root->bounds().width() + 100, root->bounds().height() + 100));
     EXPECT_EQ(InputHandler::ScrollStarted,
-              root->TryScroll(gfx::PointF(0.0f, 1.0f), InputHandler::Gesture));
+              scroll_layer->TryScroll(gfx::PointF(0.0f, 1.0f),
+                                      InputHandler::Gesture));
 
-    root->SetMaxScrollOffset(gfx::Vector2d(0, 0));
+    // Set max_scroll_offset = (0, 0).
+    scroll_layer->SetBounds(root->bounds());
     EXPECT_EQ(InputHandler::ScrollIgnored,
-              root->TryScroll(gfx::PointF(0.0f, 1.0f), InputHandler::Gesture));
+              scroll_layer->TryScroll(gfx::PointF(0.0f, 1.0f),
+                                      InputHandler::Gesture));
 
-    root->SetMaxScrollOffset(gfx::Vector2d(-100, -100));
+    // Set max_scroll_offset = (-100, -100).
+    scroll_layer->SetBounds(gfx::Size());
     EXPECT_EQ(InputHandler::ScrollIgnored,
-              root->TryScroll(gfx::PointF(0.0f, 1.0f), InputHandler::Gesture));
+              scroll_layer->TryScroll(gfx::PointF(0.0f, 1.0f),
+                                      InputHandler::Gesture));
 
     EndTest();
   }
@@ -1093,8 +1196,9 @@ class LayerTreeHostScrollTestLayerStructureChange
     scroll_layer->SetPosition(gfx::Point(0, 0));
     scroll_layer->SetAnchorPoint(gfx::PointF());
     scroll_layer->SetIsDrawable(true);
-    scroll_layer->SetScrollable(true);
-    scroll_layer->SetMaxScrollOffset(gfx::Vector2d(100, 100));
+    scroll_layer->SetScrollClipLayer(parent);
+    scroll_layer->SetBounds(gfx::Size(parent->bounds().width() + 100,
+                                      parent->bounds().height() + 100));
     scroll_layer->set_did_scroll_callback(base::Bind(
         &FakeLayerScrollClient::DidScroll, base::Unretained(client)));
     client->owner_ = this;