Add migration to WebAssembly information to PNaCl / NaCl docs.

native_client_sdk/doc_generated/sdk/release-notes.html

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-<section id="release-notes">
-<span id="sdk-release-notes"></span><h1 id="release-notes"><span id="sdk-release-notes"></span>Release Notes</h1>
+<b><font color="#cc0000">
+NOTE:
+Deprecation of the technologies described here has been announced
+for platforms other than ChromeOS.<br/>
+Please visit our
+<a href="/native-client/migration">migration guide</a>
+for details.
+</font></b>
+<hr/><section id="release-notes">
+<h1 id="release-notes">Release Notes</h1>
 <p>The dates in the following release notes denote when Chrome and the NaCl SDK
 reached canary status. The stable release is typically 6 weeks later.</p>
 <h2 id="chrome-pepper-49">Chrome/Pepper 49</h2>
 <ul class="small-gap">
 <li>GCC-based newlib toolchains removed from the SDK.  These have been
 superseded by the nacl-clang toolchain which also produces statically linked
 architecture specific nexe files.</li>
 <li>gtest/gmock no longer shipped as pre-built libraries.  This is in-line with
 normal gtest/gmock usage guidelines.  Projects wishing to use gtest/gmock must
 now add explicit include paths and compile gtest-all.cc locally.</li>
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 <a class="reference internal" href="/native-client/devguide/devcycle/debugging.html#debugging-pnacl-pexes"><em>BC files with debug metadata in the browser</em></a>,
 remember that debug info from SDK version <code>X</code> is only compatible with the
 PNaCl translator in chrome version <code>X</code>. The bitcode debug metadata format
 changed from LLVM 3.5 to 3.6. If you need to debug an app built with SDK
 version <code>X</code> running in Chrome version <code>Y</code> (with <code>X != Y</code>), it is still
 possible to do so. Simply translate the pexe to a nexe using the
 <a class="reference internal" href="/native-client/devguide/devcycle/debugging.html#debugging-pexes-via-nexes"><em>offline pnacl-translate tool from SDK version X</em></a> instead of using the translator in the
 browser (version <code>Y</code>).</li>
 <li>PNaCl&#8217;s support for use of libstdc++ 4.6 as the C++ standard library is
 deprecated and will be removed in the next release. PNaCl has used libc++
-(which is much more up-to-date, currently based on LLVM 3.6) as the default
+(which is much more up to date, currently based on LLVM 3.6) as the default
 since Pepper 33.</li>
 <li>PNaCl&#8217;s experimental <a class="reference external" href="https://chromium.googlesource.com/native_client/pnacl-subzero/+/master/README.rst">Subzero translator</a> is available for x86-32 NaCl in
 Chrome version 43, behind a flag. To give it a try, run Chrome with the
 <code>--enable-pnacl-subzero</code> commandline flag, and use the <code>optlevel 0</code>
 <a class="reference internal" href="/native-client/reference/nacl-manifest-format.html#pnacl-nmf-optlevels"><em>NaCl manifest option</em></a>. Application startup time
 should be several times faster than the previous LLVM-based <code>optlevel 0</code>
 mode, with similar code quality. Note that x86-32 NaCl requires a 32-bit
 Chrome. On Windows, it also requires a 32-bit Windows OS, but 64-bit Linux
 OSes can run x86-32 NaCl. If you try it out, please send us feedback
 on <a class="reference external" href="https://groups.google.com/forum/#!forum/native-client-dev">native-client-dev</a>. We are working on improvements and adding
@@ skipping 599 matching lines @@
 </ul>
 <h3 id="id31">PPAPI</h3>
 <ul class="small-gap">
 <li>The <code>CompletionCallbackFactory</code> class template now takes a thread traits
 class as its second parameter. For details see the <a class="reference external" href="/native-client/pepper_stable/cpp/classpp_1_1_completion_callback_factory#details">CompletionCallbackFactory
 class template reference</a>.</li>
 </ul>
 </section>
 
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