Add support for path rendering functions with CHROMIUM_path_rendering in
gpu command buffer. CHROMIUM_path_rendering pseudo extension will use
NV_path_rendering (NVPR).

After this patch, CHROMIUM_path_rendering is able to draw solid color
paths.

Adds following functions to the command buffer:
glGenPathsCHROMIUM
glDeletePathsCHROMIUM
glIsPathCHROMIUM
glPathCommandsCHROMIUM
glPathParameterfCHROMIUM
glPathParameteriCHROMIUM
glPathStencilFuncCHROMIUM
glStencilFillPathCHROMIUM
glStencilStrokePathCHROMIUM
glCoverFillPathCHROMIUM
glCoverStrokePathCHROMIUM
glStencilThenCoverFillPathCHROMIUM
glStencilThenCoverStrokePathCHROMIUM

Noteworthy items:

NVPR has calls with multiple data arrays. These will be passed by
memcpy:ing the arrays into the same transfer buffer. The arrays
containing GLfloats are copied first, because floats have more strict
alignment needs than whatever is in the other array.

The functions exposed by the command buffer take in subset of the values
that plain NVPR functions accept. Also some functions do not take
exact same amount of parameters, rather only those parameters that
are expected to vary based on Skia implementation.

The change does not add vertexshader-less shader program support to the
command buffer. The caller is expected to use a dummy vertex
shader. NVPR calls will ignore the vertex shader.

Adds gpu::gles2::PathManager class that should be similar to other
resource manager classes. The intention is that paths can be shared in
similar manner as other resources.

Changes generator to generate feature_info check for Is -type of
functions.

Moves the path matrix related constants from glchromium.h to
gl2extchromium.h, the constants are not "normal" GLES constants, rather
they are part of the extension.

Skia will not yet use the extension, because texturing support and
instanced variants of the draw functions are not exposed by
CHROMIUM_path_rendering.

The extension will be available through flag --enable-gl-path-rendering
BUG=344330

Review URL: https://codereview.chromium.org/169403005

Cr-Commit-Position: refs/heads/master@{#338666}