[mojo] Get rid of Skia type converters

ui/gfx/ipc/gfx_param_traits.cc

Index: ui/gfx/ipc/gfx_param_traits.cc
diff --git a/ui/gfx/ipc/gfx_param_traits.cc b/ui/gfx/ipc/gfx_param_traits.cc
index a49e1da95980c0d1406080cf28ecfb2a52b49622..907231d2652e3b15a450b7cff61e37db6adb607b 100644
--- a/ui/gfx/ipc/gfx_param_traits.cc
+++ b/ui/gfx/ipc/gfx_param_traits.cc
@@ -256,7 +256,11 @@ void ParamTraits<gfx::RectF>::Log(const gfx::RectF& p, std::string* l) {
                                p.width(), p.height()));
 }
 
-void ParamTraits<SkBitmap>::Write(Message* m, const SkBitmap& p) {
+size_t ParamTraits<SkBitmap>::GetSize(const SkBitmap& p) {

[Ken Rockot(use gerrit already), 2016/02/01 17:57:01]

NOTE to tsepez@: Defining a GetSize() trait is a prerequisite for using a
ParamTraits<T> as a serializer on top of Mojo, because we always preallocate
buffers for Mojo messages. I was thinking it might reduce errors to add a
base::PickleSizer type with an interface analogous to base::Pickle but which
just computes payload size, then we could pass that to GetSize instead of asking
developers to compute it 100% manually.

Alternatively we could make Pickle's interfaces virtual, have a new Pickle impl
just for computing size, and feed that directly to ParamTraits<T>::Write for a
first pass. I've been avoiding that approach because I didn't want to add vtable
lookups to such frequently called methods.

WDYT?

[Tom Sepez, 2016/02/01 18:31:58]

I prefer the first approach, I wouldn't be fond of adding virtual calls to
pickle.

+  return sizeof(int32_t) * 2 + sizeof(SkBitmap_Data) + p.getSize();

[jam, 2016/02/01 17:53:48]

I'd expect this to match the Write method below, why the difference?

i.e. the "sizeof(SkBitmap_Data) + p.getSize();" parts correspond to the two
WriteData calls, but where is the "sizeof(int32_t)" calls coming from?

+}
+
+void ParamTraits<SkBitmap>::Write(base::Pickle* m, const SkBitmap& p) {
   size_t fixed_size = sizeof(SkBitmap_Data);
   SkBitmap_Data bmp_data;
   bmp_data.InitSkBitmapDataForTransfer(p);
@@ -268,7 +272,7 @@ void ParamTraits<SkBitmap>::Write(Message* m, const SkBitmap& p) {
                static_cast<int>(pixel_size));
 }
 
-bool ParamTraits<SkBitmap>::Read(const Message* m,
+bool ParamTraits<SkBitmap>::Read(const base::Pickle* m,
                                  base::PickleIterator* iter,
                                  SkBitmap* r) {
   const char* fixed_data;