don't reallocate the mesh each time we use it

the Mesh object can be part of each Layer (at least currently).
also reworked the Mesh code a bit to make it easier to access
the vertex data.

Change-Id: I0490851ba898f0aa2e55b62958dcd8bdb535e98b
diff --git a/services/surfaceflinger/RenderEngine/Mesh.cpp b/services/surfaceflinger/RenderEngine/Mesh.cpp
index a08eea6..3f50cb0 100644
--- a/services/surfaceflinger/RenderEngine/Mesh.cpp
+++ b/services/surfaceflinger/RenderEngine/Mesh.cpp
@@ -30,23 +30,15 @@
     delete [] mVertices;
 }
 
-float const* Mesh::operator[](size_t index) const {
-    return &mVertices[index * mStride];
-}
-
-float* Mesh::operator[](size_t index) {
-    return &mVertices[index * mStride];
-}
-
 Mesh::Primitive Mesh::getPrimitive() const {
     return mPrimitive;
 }
 
 
-float const* Mesh::getVertices() const {
+float const* Mesh::getPositions() const {
     return mVertices;
 }
-float* Mesh::getVertices() {
+float* Mesh::getPositions() {
     return mVertices;
 }