Started adding links for Canvas and its 2D and WebGL contexts.

third_party/WebKit/Source/SpecMapping.md

Index: third_party/WebKit/Source/SpecMapping.md
diff --git a/third_party/WebKit/Source/SpecMapping.md b/third_party/WebKit/Source/SpecMapping.md
index 0e2151f9e2d67941ef26ac2a53bb82dcfc330022..62f38ae5a1172805a058e25be30f5cd3c8ff1b95 100644
--- a/third_party/WebKit/Source/SpecMapping.md
+++ b/third_party/WebKit/Source/SpecMapping.md
@@ -2,7 +2,7 @@
 
 Blink is Chromium's implementation of the open web platform. This document
 attempts to map terms and concepts found in the specification of the open web
-platfrom to classes and files found in Blink's source tree.
+platform to classes and files found in Blink's source tree.
 
 [TOC]
 
@@ -16,3 +16,27 @@ A browsing context corresponds to the
 [DOMWindow](https://cs.chromium.org/Source/core/frame/DOMWindow.h) interface
 where the main implementation is
 [LocalDOMWindow](https://cs.chromium.org/Source/core/frame/LocalDOMWindow.h).
+
+### [canvas](https://html.spec.whatwg.org/multipage/scripting.html#the-canvas-element)
+
+An HTML element into which drawing can be performed imperatively via
+JavaScript. Multiple
+[context types](https://html.spec.whatwg.org/multipage/scripting.html#dom-canvas-getcontext)
+are supported for different use cases.
+
+The main element's sources are in
+[HTMLCanvasElement](https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/html/HTMLCanvasElement.h). Contexts
+are implemented via modules. The top-level module is
+[HTMLCanvasElementModule](https://cs.chromium.org/chromium/src/third_party/WebKit/Source/modules/canvas/HTMLCanvasElementModule.h).
+
+The
+[2D canvas context](https://html.spec.whatwg.org/multipage/scripting.html#canvasrenderingcontext2d)
+is implemented in
+[modules/canvas2d](https://cs.chromium.org/chromium/src/third_party/WebKit/Source/modules/canvas2d/).

[Justin Novosad, 2016/09/22 20:40:45]

There is also the bitmap renderer context that lives
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/modules/imageb...

+
+The
+[WebGL 1.0](https://www.khronos.org/registry/webgl/specs/latest/1.0/)
+and
+[WebGL 2.0](https://www.khronos.org/registry/webgl/specs/latest/2.0/)
+contexts ([Github repo](https://github.com/KhronosGroup/WebGL)) are
+implemented in [modules/webgl](https://cs.chromium.org/chromium/src/third_party/WebKit/Source/modules/webgl/).