android: Pass CPU properties from browser to renderer process.

base/android/java/src/org/chromium/base/CpuFeatures.java

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.base;
+
+// The only purpose of this class is to allow sending CPU properties
+// from the browser process to sandboxed renderer processes. This is
+// needed because sandboxed processes cannot, on ARM, query the kernel
+// about the CPU's properties by parsing /proc, so this operation must
+// be performed in the browser process, and the result passed to
+// renderer ones.
+//
+// For more context, see crbug.com/164154

[joth, 2012/12/19 19:09:40]

nit: linkify.

[digit1, 2013/01/09 11:26:19]

Sure, will do.

+//
+// Technically, this is a wrapper around the native NDK cpufeatures
+// library. The exact CPU features bits are never used in Java so
+// there is no point in duplicating their definitions here.
+//
+@JNINamespace("base::android")
+public abstract class CpuFeatures {
+    /**
+     * Return the number of CPU Cores on the device.
+     */
+    public static int getCount() {
+        return nativeGetCoreCount();
+    }
+
+    /**
+     * Return the CPU feature mask.
+     * This is a 64-bit integer that corresponds to the CPU's features.
+     * The value is taken directory to

[agl, 2012/12/19 18:26:36]

Comment seems truncated?

[digit1, 2013/01/09 11:26:19]

Yes, I'll update it.

+     */
+     public static long getMask() {
+        return nativeGetCpuFeatures();
+     }
+
+    /**
+     * Set CPU core count and feature mask.
+     * This must be called in sandboxed renderer processes before any
+     * other function from the native library that might depend on the
+     * the CPU count / features.
+     * @param coreCount Number of CPU cores on device.
+     * @param featuresMask CPU features mask.
+     */
+    public static void set(int coreCount, long featuresMask) {

[joth, 2012/12/19 19:09:40]

is this needed? loos like the sandbox process is already calling straight to the
native method.

[digit1, 2013/01/09 11:26:19]

Indeed, this is no longer needed.

+        nativeSetCpu(coreCount, featuresMask);
+    }
+
+    private static native int nativeGetCoreCount();
+    private static native long nativeGetCpuFeatures();
+    private static native void nativeSetCpu(int coreCount, long featuresMask);
+}