[vr] Add incognito coloring

chrome/browser/android/vr_shell/vr_shell_renderer.cc

Index: chrome/browser/android/vr_shell/vr_shell_renderer.cc
diff --git a/chrome/browser/android/vr_shell/vr_shell_renderer.cc b/chrome/browser/android/vr_shell/vr_shell_renderer.cc
index 098e8608e5fd3364988a4c8137f444cf82f700dc..3632b710ed0f742faa1536d63b6d03f53fdb8191 100644
--- a/chrome/browser/android/vr_shell/vr_shell_renderer.cc
+++ b/chrome/browser/android/vr_shell/vr_shell_renderer.cc
@@ -138,7 +138,8 @@ const char* GetShaderSource(vr_shell::ShaderID shader) {
                 vec2(u_CopyRect[0] + v_TexCoordinate.x * u_CopyRect[2],
                      u_CopyRect[1] + v_TexCoordinate.y * u_CopyRect[3]);
             lowp vec4 color = texture2D(u_Texture, scaledTex);
-            gl_FragColor = vec4(color.xyz, color.w * opacity);
+            // premultiply opacity

[tiborg, 2017/05/25 00:47:18]

Nit: capital P and period in the end.

+            gl_FragColor = color * opacity;
           }
           /* clang-format on */);
     case vr_shell::ShaderID::WEBVR_VERTEX_SHADER:
@@ -251,7 +252,8 @@ const char* GetShaderSource(vr_shell::ShaderID shader) {
 
           void main() {
             lowp vec4 texture_color = texture2D(u_texture, v_TexCoordinate);
-            gl_FragColor = vec4(texture_color.xyz, texture_color.w * u_Opacity);
+            // premultiply alpha

[tiborg, 2017/05/25 00:47:18]

Here too.

+            gl_FragColor = texture_color * u_Opacity;
           }
           /* clang-format on */);
     default:
@@ -415,7 +417,8 @@ void TexturedQuadRenderer::Flush() {
   glEnableVertexAttribArray(tex_coord_handle_);
 
   glEnable(GL_BLEND);
-  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+  // Our textures have premultiplied alpha

[tiborg, 2017/05/25 00:47:18]

Nit: period in the end.

+  glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
 
   // Link texture data with texture unit.
   glActiveTexture(GL_TEXTURE0);
@@ -667,7 +670,8 @@ void ControllerRenderer::Draw(VrControllerModel::State state,
   glEnableVertexAttribArray(tex_coord_handle_);
 
   glEnable(GL_BLEND);
-  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+  // Our textures have premultiplied alpha.
+  glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
 
   glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indices_buffer_);