Update linux go to 1.15beta1

From https://ci.android.com/builds/submitted/6626886/linux/latest/go.zip

Test: m blueprint_tools
Change-Id: Ib0d1176e769611b25554177aef209bc7e6456694
diff --git a/doc/install-source.html b/doc/install-source.html
index 12b10d5..b5b422e 100644
--- a/doc/install-source.html
+++ b/doc/install-source.html
@@ -33,80 +33,64 @@
 </p>
 
 <p>
-The Go compilers support nine instruction sets.
-There are important differences in the quality of the compilers for the different
-architectures.
-</p>
+The Go compilers support twelve instruction sets:
 
 <dl>
 <dt>
-	<code>amd64</code> (also known as <code>x86-64</code>)
+  <code>amd64</code>, <code>386</code>
 </dt>
 <dd>
-	A mature implementation.
+  The <code>x86</code> instruction set, 64- and 32-bit.
 </dd>
 <dt>
-	<code>386</code> (<code>x86</code> or <code>x86-32</code>)
+  <code>arm64</code>, <code>arm</code>
 </dt>
 <dd>
-	Comparable to the <code>amd64</code> port.
+  The <code>ARM</code> instruction set, 64-bit (<code>AArch64</code>) and 32-bit.
 </dd>
 <dt>
-	<code>arm</code> (<code>ARM</code>)
+  <code>ppc64</code>, <code>ppc64le</code>
 </dt>
 <dd>
-	Supports Linux, FreeBSD, NetBSD, OpenBSD and Darwin binaries. Less widely used than the other ports.
+  The 64-bit PowerPC instruction set, big- and little-endian.
 </dd>
 <dt>
-	<code>arm64</code> (<code>AArch64</code>)
+  <code>s390x</code>
 </dt>
 <dd>
-	Supports Linux and Darwin binaries. New in 1.5 and not as well exercised as other ports.
+  The IBM z/Architecture.
 </dd>
 <dt>
-	<code>ppc64, ppc64le</code> (64-bit PowerPC big- and little-endian)
+  <code>mips64</code>, <code>mips64le</code>, <code>mips</code>,  <code>mipsle</code>
 </dt>
 <dd>
-	Supports Linux binaries. New in 1.5 and not as well exercised as other ports.
+  The <code>MIPS</code> instruction set, big- and little-endian, 64- and 32-bit.
 </dd>
 <dt>
-	<code>mips, mipsle</code> (32-bit MIPS big- and little-endian)
+  <code>wasm</code>
 </dt>
 <dd>
-	Supports Linux binaries. New in 1.8 and not as well exercised as other ports.
-</dd>
-<dt>
-	<code>mips64, mips64le</code> (64-bit MIPS big- and little-endian)
-</dt>
-<dd>
-	Supports Linux binaries. New in 1.6 and not as well exercised as other ports.
-</dd>
-<dt>
-	<code>s390x</code> (IBM System z)
-</dt>
-<dd>
-	Supports Linux binaries. New in 1.7 and not as well exercised as other ports.
-</dd>
-<dt>
-	<code>wasm</code> (WebAssembly)
-</dt>
-<dd>
-	Targets the WebAssembly platform. New in 1.11 and not as well exercised as other ports.
+  <a href="https://webassembly.org">WebAssembly</a>.
 </dd>
 </dl>
-
-<p>
-Except for things like low-level operating system interface code, the run-time
-support is the same in all ports and includes a mark-and-sweep garbage
-collector, efficient array and string slicing, and support for efficient
-goroutines, such as stacks that grow and shrink on demand.
 </p>
 
 <p>
-The compilers can target the DragonFly BSD, FreeBSD, Linux, NetBSD, OpenBSD,
-macOS (Darwin), Plan 9, Solaris and Windows operating systems.
-The full set of supported combinations is listed in the discussion of
-<a href="#environment">environment variables</a> below.
+The compilers can target the AIX, Android, DragonFly BSD, FreeBSD,
+Illumos, Linux, macOS/iOS (Darwin), NetBSD, OpenBSD, Plan 9, Solaris,
+and Windows operating systems (although not all operating systems
+support all architectures).
+</p>
+
+<p>
+A list of ports which are considered "first class" is available at the
+<a href="/wiki/PortingPolicy#first-class-ports">first class ports</a>
+wiki page.
+</p>
+
+<p>
+The full set of supported combinations is listed in the
+discussion of <a href="#environment">environment variables</a> below.
 </p>
 
 <p>
@@ -122,23 +106,17 @@
 
 </div>
 
-<h2 id="go14">Install Go compiler binaries</h2>
+<h2 id="go14">Install Go compiler binaries for bootstrap</h2>
 
 <p>
 The Go toolchain is written in Go. To build it, you need a Go compiler installed.
-The scripts that do the initial build of the tools look for an existing Go tool
-chain in <code>$GOROOT_BOOTSTRAP</code>.
-If unset, the default value of <code>GOROOT_BOOTSTRAP</code>
-is <code>$HOME/go1.4</code>.
-</p>
-
-<p>
-There are many options for the bootstrap toolchain.
-After obtaining one, set <code>GOROOT_BOOTSTRAP</code> to the
-directory containing the unpacked tree.
-For example, <code>$GOROOT_BOOTSTRAP/bin/go</code> should be
-the <code>go</code> command binary for the bootstrap toolchain.
-</p>
+The scripts that do the initial build of the tools look for a "go" command
+in <code>$PATH</code>, so as long as you have Go installed in your
+system and configured in your <code>$PATH</code>, you are ready to build Go
+from source. 
+Or if you prefer you can set <code>$GOROOT_BOOTSTRAP</code> to the
+root of a Go installation to use to build the new Go toolchain;
+<code>$GOROOT_BOOTSTRAP/bin/go</code> should be the go command to use.</p>
 
 <h3 id="bootstrapFromBinaryRelease">Bootstrap toolchain from binary release</h3>
 
@@ -263,10 +241,12 @@
 the default location of <code>$GOPATH</code>.
 See <a href="#gopath"><code>GOPATH</code></a> below.</p>
 
+<p>
 Reminder: If you opted to also compile the bootstrap binaries from source (in an
 earlier section), you still need to <code>git clone</code> again at this point
 (to checkout the latest <code>&lt;tag&gt;</code>), because you must keep your
 go1.4 repository distinct.
+</p>
 
 <h2 id="head">(Optional) Switch to the master branch</h2>
 
@@ -521,7 +501,7 @@
 
 <p>
 Choices for <code>$GOOS</code> are
-<code>android</code>, <code>darwin</code> (macOS 10.11 and above and iOS),
+<code>android</code>, <code>darwin</code> (macOS/iOS),
 <code>dragonfly</code>, <code>freebsd</code>, <code>illumos</code>, <code>js</code>,
 <code>linux</code>, <code>netbsd</code>, <code>openbsd</code>,
 <code>plan9</code>, <code>solaris</code> and <code>windows</code>.
@@ -560,15 +540,9 @@
 <td></td><td><code>android</code></td> <td><code>arm64</code></td>
 </tr>
 <tr>
-<td></td><td><code>darwin</code></td> <td><code>386</code></td>
-</tr>
-<tr>
 <td></td><td><code>darwin</code></td> <td><code>amd64</code></td>
 </tr>
 <tr>
-<td></td><td><code>darwin</code></td> <td><code>arm</code></td>
-</tr>
-<tr>
 <td></td><td><code>darwin</code></td> <td><code>arm64</code></td>
 </tr>
 <tr>