Add simpler reading methods to Blob interface. (#117)

* Add simpler reading methods to Blob interface.

This fixes #40

index.bs

@@ -65,6 +65,9 @@ spec: url
     text: url; for:/
   type: interface
     text: URL
+spec: fetch
+  type:interface
+    text:ReadableStream
 </pre>
 
 <pre class="anchors">
@@ -215,7 +218,7 @@ which must be initially set to the state of the underlying storage,
 if any such underlying storage exists.
 Further normative definition of <a>snapshot state</a> can be found for {{File}}s.
 
-<pre class="idl">
+<xmp class="idl">
 [Constructor(optional sequence&lt;BlobPart> blobParts,
              optional BlobPropertyBag options),
  Exposed=(Window,Worker), Serializable]
@@ -228,6 +231,11 @@ interface Blob {
   Blob slice(optional [Clamp] long long start,
             optional [Clamp] long long end,
             optional DOMString contentType);
+
+  // read from the Blob.
+  [NewObject] ReadableStream stream();
+  [NewObject] Promise<USVString> text();
+  [NewObject] Promise<ArrayBuffer> arrayBuffer();
 };
 
 enum EndingType { "transparent", "native" };
@@ -238,7 +246,7 @@ dictionary BlobPropertyBag {
 };
 
 typedef (BufferSource or Blob or USVString) BlobPart;
-</pre>
+</xmp>
 
 {{Blob}} objects are [=serializable objects=]. Their [=serialization steps=],
 given |value| and |serialized|, are:
@@ -561,6 +569,38 @@ It must act as follows:
   </pre>
 </div>
 
+### The {{Blob/stream()}} method ### {#stream-method-algo}
+
+The <dfn method for=Blob>stream()</dfn> method, when invoked, must return
+the result of calling [=get stream=] on the [=context object=].
+
+### The {{Blob/text()}} method ### {#text-method-algo}
+
+The <dfn method for=Blob>text()</dfn> method, when invoked, must run these steps:
+
+1. Let |stream| be the result of calling [=get stream=] on the [=context object=].
+1. Let |reader| be the result of [=get a reader|getting a reader=] from |stream|.
+   If that threw an exception, return a new promise rejected with that exception.
+1. Let |promise| be the result of [=read all bytes|reading all bytes=] from |stream| with |reader|.
+1. Return the result of transforming |promise| by a fulfillment handler that returns the result of
+   running [=UTF-8 decode=] on its first argument.
+
+Note: This is different from the behavior of {{FileReader/readAsText()}} to align better
+with the behavior of {{Body/text()|Fetch's text()}}. Specifically this method will always
+use UTF-8 as encoding, while {{FileReader}} can use a different encoding depending on
+the blob's type and passed in encoding name.
+
+### The {{Blob/arrayBuffer()}} method ### {#arraybuffer-method-algo}
+
+The <dfn method for=Blob>arrayBuffer()</dfn> method, when invoked, must run these steps:
+
+1. Let |stream| be the result of calling [=get stream=] on the [=context object=].
+1. Let |reader| be the result of [=get a reader|getting a reader=] from |stream|.
+   If that threw an exception, return a new promise rejected with that exception.
+1. Let |promise| be the result of [=read all bytes|reading all bytes=] from |stream| with |reader|.
+1. Return the result of transforming |promise| by a fulfillment handler that returns
+   a new {{ArrayBuffer}} whose contents are its first argument.
+
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