ash: Never associate an internal touchscreen with an external display

BUG=515201
TEST=TouchscreenUtilTest.TestWithNoInternalDisplay updated to reflect
that internal touchscreen should not be associated with any display.

Review URL: https://codereview.chromium.org/1254413010

Cr-Commit-Position: refs/heads/master@{#341564}

ash/touch/touchscreen_util.cc

@@ -27,8 +27,10 @@ void AssociateTouchscreens(std::vector<DisplayInfo>* displays,
 
   std::set<int> no_match_touchscreen;
   for (size_t i = 0; i < devices.size(); ++i) {
-    if (internal_state &&
-        devices[i].type == ui::InputDeviceType::INPUT_DEVICE_INTERNAL) {
+    if (devices[i].type == ui::InputDeviceType::INPUT_DEVICE_INTERNAL) {
+      // Don't try and map internal touchscreens to external displays.
+      if (!internal_state)
+        continue;
       VLOG(2) << "Found internal device for display " << internal_state->id()
               << " with device id " << devices[i].id << " size "
               << devices[i].size.ToString();

ash/touch/touchscreen_util_unittest.cc

@@ -226,12 +226,12 @@ TEST_F(TouchscreenUtilTest, TestWithNoInternalDisplay) {
       ui::TouchscreenDevice(2, ui::InputDeviceType::INPUT_DEVICE_INTERNAL, "",
                             gfx::Size(9999, 888), 0));
 
+  // Internal touchscreen should not be associated with any display
   AssociateTouchscreens(&displays_, devices);
 
   EXPECT_EQ(1u, displays_[0].input_devices().size());
   EXPECT_EQ(1, displays_[0].input_devices()[0]);
-  EXPECT_EQ(1u, displays_[1].input_devices().size());
-  EXPECT_EQ(2, displays_[1].input_devices()[0]);
+  EXPECT_EQ(0u, displays_[1].input_devices().size());
   EXPECT_EQ(0u, displays_[2].input_devices().size());
   EXPECT_EQ(0u, displays_[3].input_devices().size());
 }