Fix GN build with missing ShaderVars.cpp.
Fix GN build with missing ShaderVars.cpp.

Change-Id: I29be6cdda643f83a40a6adc9b76153667aafcc51
Reviewed-on: https://chromium-review.googlesource.com/211400
Tested-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Reviewed-by: Zhenyao Mo <655bdf1d95ff956cd68886dd9e86ee5e987c9dbb@chromium.org>

geekboxzone/lollipop_external_chromium_org_third_party_angle,domokit/waterfall,ghostoy/angle,xin3liang/platform_external_chromium_org_third_party_angle,nandhanurrevanth/angle,crezefire/angle,ppy/angle,crezefire/angle,jgcaaprom/android_external_chromium_org_third_party_angle,mikolalysenko/angle,vvuk/angle,crezefire/angle,xin3liang/platform_external_chromium_org_third_party_angle,android-ia/platform_external_chromium_org_third_party_angle,MSOpenTech/angle,ecoal95/angle,vvuk/angle,larsbergstrom/angle,mybios/angle,ecoal95/angle,ecoal95/angle,ppy/angle,ppy/angle,nandhanurrevanth/angle,ppy/angle,jgcaaprom/android_external_chromium_org_third_party_angle,mrobinson/rust-angle,csa7mdm/angle,mybios/angle,MIPS/external-chromium_org-third_party-angle,mybios/angle,nandhanurrevanth/angle,ecoal95/angle,android-ia/platform_external_chromium_org_third_party_angle,MIPS/external-chromium_org-third_party-angle,domokit/waterfall,xin3liang/platform_external_chromium_org_third_party_angle,bsergean/angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,nandhanurrevanth/angle,MIPS/external-chromium_org-third_party-angle,mrobinson/rust-angle,xin3liang/platform_external_chromium_org_third_party_angle,mikolalysenko/angle,ghostoy/angle,mrobinson/rust-angle,vvuk/angle,mlfarrell/angle,android-ia/platform_external_chromium_org_third_party_angle,ecoal95/angle,crezefire/angle,mrobinson/rust-angle,MIPS/external-chromium_org-third_party-angle,android-ia/platform_external_chromium_org_third_party_angle,csa7mdm/angle,mlfarrell/angle,mybios/angle,ghostoy/angle,ghostoy/angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,bsergean/angle,mrobinson/rust-angle,MSOpenTech/angle,mikolalysenko/angle,bsergean/angle,larsbergstrom/angle,csa7mdm/angle,csa7mdm/angle,vvuk/angle,MSOpenTech/angle,mikolalysenko/angle,larsbergstrom/angle,bsergean/angle,jgcaaprom/android_external_chromium_org_third_party_angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,jgcaaprom/android_external_chromium_org_third_party_angle,larsbergstrom/angle,mlfarrell/angle,mlfarrell/angle,MSOpenTech/angle