cc: Support texture rect targets for masks

Currently, GLRenderer supports tile resources as either texture 2d or
texture rectangle.  Before this patch, it only supported texture 2d
masks.  This fills the gap to handle texture rectangle masks.  In
practice it means that using a zero copy raster worker pool will
now not break masks.  This in turn enables impl-side painting for
layout tests.

Unfortunately, there is a lot of indirection between a test saying it
wants to test a particular target type and what needs to happen.  To
make sure that tests are testing the right thing, the creation of
the raster worker and resource pools is now virtual so that tests
can create them as explicitly as needed.

R=danakj@chromium.org,reveman@chromium.org
BUG=423533

Review URL: https://codereview.chromium.org/668123003

Cr-Commit-Position: refs/heads/master@{#302010}

diff --git a/cc/BUILD.gn b/cc/BUILD.gn
index e1bd12f..32d6aed 100644
--- a/cc/BUILD.gn
+++ b/cc/BUILD.gn

@@ -571,6 +571,8 @@
     "test/layer_tree_host_common_test.h",
     "test/layer_tree_json_parser.cc",
     "test/layer_tree_json_parser.h",
+    "test/layer_tree_pixel_resource_test.cc",
+    "test/layer_tree_pixel_resource_test.h",
     "test/layer_tree_pixel_test.cc",
     "test/layer_tree_pixel_test.h",
     "test/layer_tree_test.cc",