Android M low ram device优化apk安装速度

安装apk慢是因为dex2oat行为导致的，要优化可以牺牲一些检查，强制用vmSafeMode去安装，facebook举例，低端机器从安装10分钟改善为1分钟不到。修改方法如下：
1 diff --git a/base/services/core/java/com/android/server/pm/PackageDexOptimizer.java b/base/services/core/java/com/android/server/pm/PackageDexOptimizer.java
2 index f35552d..8ae1e13 100644
3 --- a/base/services/core/java/com/android/server/pm/PackageDexOptimizer.java
4 +++ b/base/services/core/java/com/android/server/pm/PackageDexOptimizer.java
5 @@ -115,7 +115,12 @@ final class PackageDexOptimizer {
6 return DEX_OPT_SKIPPED;
7 }
8
9 +/*
10 final boolean vmSafeMode = (pkg.applicationInfo.flags & ApplicationInfo.FLAG_VM_SAFE_MODE) != 0;
11 + */
12 + boolean vmSafeMode = (pkg.applicationInfo.flags & ApplicationInfo.FLAG_VM_SAFE_MODE) != 0;
13 final boolean debuggable = (pkg.applicationInfo.flags & ApplicationInfo.FLAG_DEBUGGABLE) != 0;
14
15 final List<String> paths = pkg.getAllCodePathsExcludingResourceOnly();
16 @@ -171,6 +176,13 @@ final class PackageDexOptimizer {
17 throw new IllegalStateException("Invalid dexopt needed: " + dexoptNeeded);
18 }
19
20 + if (pkg.applicationInfo.packageName.contains("facebook")) {
21 + vmSafeMode = true;
22 + }
23 Log.i(TAG, "Running dexopt (" + dexoptType + ") on: " + path + " pkg="
24 + pkg.applicationInfo.packageName + " isa=" + dexCodeInstructionSet
25 + " vmSafeMode=" + vmSafeMode + " debuggable=" + debuggable