gl: Add swiftshader as a data-dep to gl.

This allows turning on enable_swiftshader in 'gn args', and building,
for example, mus, and have the swiftshader also built correctly.

BUG=none
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2925333003
Cr-Commit-Position: refs/heads/master@{#478498}

content/browser/BUILD.gn

@@ -1688,7 +1688,6 @@ source_set("browser") {
     deps += [
       "//third_party/iaccessible2",
       "//third_party/isimpledom",
-      "//third_party/swiftshader",
     ]
     libs += [
       "comctl32.lib",
@@ -1837,11 +1836,6 @@ source_set("browser") {
     deps += [ "//ui/gfx/x" ]
   }
 
-  if (is_linux && !is_chromeos && use_x11 &&
-      (target_cpu == "x86" || target_cpu == "x64")) {
-    deps += [ "//third_party/swiftshader" ]
-  }
-
   if (use_pango) {
     configs += [ "//build/config/linux/pangocairo" ]
   }

ui/gl/BUILD.gn

@@ -153,6 +153,10 @@ component("gl") {
     "//ui/gfx/geometry",
   ]
 
+  data_deps = []
+  if (enable_swiftshader) {
+    data_deps += [ "//third_party/swiftshader" ]
+  }
   if (use_egl) {
     sources += [
       "angle_platform_impl.cc",
@@ -198,7 +202,7 @@ component("gl") {
 
     deps += [ "//ui/base/x" ]
 
-    data_deps = [
+    data_deps += [
       "//third_party/angle:libEGL",
       "//third_party/angle:libGLESv2",
     ]
@@ -250,7 +254,7 @@ component("gl") {
     libs = [ "dwmapi.lib" ]
     ldflags = [ "/DELAYLOAD:dwmapi.dll" ]
 
-    data_deps = [
+    data_deps += [
       "//third_party/angle:libEGL",
       "//third_party/angle:libGLESv2",
       "//third_party/mesa:osmesa",