Migrate more functions from MathUtil to gfx::Transform

cc/gl_renderer.cc

Index: cc/gl_renderer.cc
diff --git a/cc/gl_renderer.cc b/cc/gl_renderer.cc
index 54eef96e72702b364769cb97a438d2a338211053..982d08832e4565fb2b9c8441475efe0463eb1504 100644
--- a/cc/gl_renderer.cc
+++ b/cc/gl_renderer.cc
@@ -518,7 +518,8 @@ void GLRenderer::drawRenderPassQuad(DrawingFrame& frame, const RenderPassDrawQua
 
     gfx::Transform quadRectMatrix;
     quadRectTransform(&quadRectMatrix, quad->quadTransform(), quad->rect);
-    gfx::Transform contentsDeviceTransform = MathUtil::to2dTransform(frame.windowMatrix * frame.projectionMatrix * quadRectMatrix);
+    gfx::Transform contentsDeviceTransform = frame.windowMatrix * frame.projectionMatrix * quadRectMatrix;
+    contentsDeviceTransform.FlattenTo2d();
 
     // Can only draw surface if device matrix is invertible.
     gfx::Transform contentsDeviceTransformInverse(gfx::Transform::kSkipInitialization);
@@ -664,7 +665,7 @@ void GLRenderer::drawRenderPassQuad(DrawingFrame& frame, const RenderPassDrawQua
         GLC(context(), context()->uniform3fv(shaderEdgeLocation, 8, edge));
     }
 
-    // Map device space quad to surface space. contentsDeviceTransform has no 3d component since it was generated with to2dTransform() so we don't need to project.
+    // Map device space quad to surface space. contentsDeviceTransform has no 3d component since it was flattened, so we don't need to project.
     gfx::QuadF surfaceQuad = MathUtil::mapQuad(contentsDeviceTransformInverse, deviceLayerEdges.ToQuadF(), clipped);
     DCHECK(!clipped);
 
@@ -769,7 +770,8 @@ void GLRenderer::drawTileQuad(const DrawingFrame& frame, const TileDrawQuad* qua
 
 
     gfx::QuadF localQuad;
-    gfx::Transform deviceTransform = MathUtil::to2dTransform(frame.windowMatrix * frame.projectionMatrix * quad->quadTransform());
+    gfx::Transform deviceTransform = frame.windowMatrix * frame.projectionMatrix * quad->quadTransform();
+    deviceTransform.FlattenTo2d();
     if (!deviceTransform.IsInvertible())
         return;
 
@@ -860,7 +862,7 @@ void GLRenderer::drawTileQuad(const DrawingFrame& frame, const TileDrawQuad* qua
         // Create device space quad.
         LayerQuad deviceQuad(leftEdge, topEdge, rightEdge, bottomEdge);
 
-        // Map device space quad to local space. deviceTransform has no 3d component since it was generated with to2dTransform() so we don't need to project.
+        // Map device space quad to local space. deviceTransform has no 3d component since it was flattened, so we don't need to project.
         // We should have already checked that the transform was uninvertible above.
         gfx::Transform inverseDeviceTransform(gfx::Transform::kSkipInitialization);
         bool didInvert = deviceTransform.GetInverse(&inverseDeviceTransform);