Add compositor support for half-float RGBA buffers and textures

cc/output/direct_renderer.cc

Index: cc/output/direct_renderer.cc
diff --git a/cc/output/direct_renderer.cc b/cc/output/direct_renderer.cc
index bc2b1cb782d2fe90b45a103924f0f1fcabc54393..cd4bfa5006e9eb30ab850e1dcd83f1d5b9e41ff8 100644
--- a/cc/output/direct_renderer.cc
+++ b/cc/output/direct_renderer.cc
@@ -609,9 +609,9 @@ bool DirectRenderer::UseRenderPass(DrawingFrame* frame,
   size.Enlarge(enlarge_pass_texture_amount_.width(),
                enlarge_pass_texture_amount_.height());
   if (!texture->id()) {
-    texture->Allocate(
-        size, ResourceProvider::TEXTURE_HINT_IMMUTABLE_FRAMEBUFFER,
-        resource_provider_->best_texture_format(), frame->device_color_space);
+    texture->Allocate(size,

[jbauman, 2017/02/01 23:59:21]

Is it expected that BackbufferFormat could change during the life of the
OutputSurface? If so this should check if the formats match and recreate it if
not.

+                      ResourceProvider::TEXTURE_HINT_IMMUTABLE_FRAMEBUFFER,
+                      BackbufferFormat(), frame->device_color_space);
   }
   DCHECK(texture->id());