Add java-side support for _incremental instrumentation tests

build/android/incremental_install/java/org/chromium/incrementalinstall/ClassLoaderPatcher.java

 // Copyright 2015 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.incrementalinstall;
 
 import android.content.Context;
 import android.os.Build;
 import android.util.Log;
 
@@ skipping 85 matching lines @@
         Object[] additionalElements = makeDexElements(dexFilesArr, optimizedDir);
         Reflect.setField(
                 dexPathList, "dexElements", Reflect.concatArrays(dexElements, additionalElements));
     }
 
     /**
      * Sets up all libraries within |libDir| to be loadable by System.loadLibrary().
      */
     void importNativeLibs(File libDir) throws ReflectiveOperationException, IOException {
         Log.i(TAG, "Importing native libraries from: " + libDir);
+        if (!libDir.exists()) {
+            Log.i(TAG, "No native libs exist.");
+            return;
+        }
         // The library copying is not necessary on older devices, but we do it anyways to
         // simplify things (it's fast compared to dexing).
         // https://code.google.com/p/android/issues/detail?id=79480
         File localLibsDir = new File(mAppFilesSubDir, "lib");
         File copyLibsLockFile = new File(mAppFilesSubDir, "libcopy.lock");
         if (mIsPrimaryProcess) {
             // Primary process: Copies native libraries into the app's data directory.
             ensureAppFilesSubDirExists();
             LockFile lockFile = LockFile.acquireRuntimeLock(copyLibsLockFile);
             if (lockFile == null) {
@@ skipping 46 matching lines @@
             return;
         }
         Object[] additionalElements = makeNativePathElements(newDirs);
         Reflect.setField(
                 dexPathList, "nativeLibraryPathElements",
                 Reflect.concatArrays(nativeLibraryPathElements, additionalElements));
     }
 
     private static void copyChangedFiles(File srcDir, File dstDir) throws IOException {
         // No need to delete stale libs since libraries are loaded explicitly.
+        int numNotChanged = 0;
         for (File f : srcDir.listFiles()) {
             // Note: Tried using hardlinks, but resulted in EACCES exceptions.
             File dest = new File(dstDir, f.getName());
-            copyIfModified(f, dest);
+            if (!copyIfModified(f, dest)) {
+                numNotChanged++;
+            }
+        }
+        if (numNotChanged > 0) {
+            Log.i(TAG, numNotChanged + " libs already up-to-date.");
         }
     }
 
-    private static void copyIfModified(File src, File dest) throws IOException {
+    private static boolean copyIfModified(File src, File dest) throws IOException {

[nyquist, 2016/02/10 07:08:32]

Optional nit: Add a super-tiny comment as to what the return value means?

[agrieve, 2016/02/10 16:47:15]

Electing not to since it's private and is clear from the code.

         long lastModified = src.lastModified();
         if (!dest.exists() || dest.lastModified() != lastModified) {

[nyquist, 2016/02/10 07:08:32]

Optional nit: Would it be easier to read with something like:
if (dest.exists() && dest.lastModified() == lastModified) return false;
?

[agrieve, 2016/02/10 16:47:15]

Done.

             Log.i(TAG, "Copying " + src + " -> " + dest);
             FileInputStream istream = new FileInputStream(src);
             FileOutputStream ostream = new FileOutputStream(dest);
             ostream.getChannel().transferFrom(istream.getChannel(), 0, istream.getChannel().size());
             istream.close();
             ostream.close();
             dest.setReadable(true, false);
             dest.setExecutable(true,  false);
             dest.setLastModified(lastModified);
-        } else {
-            Log.i(TAG, "Up-to-date: " + dest);
+            return true;
         }
+        return false;
     }
 
     private void ensureAppFilesSubDirExists() {
         mAppFilesSubDir.mkdir();
         mAppFilesSubDir.setExecutable(true, false);
     }
 
     private void createSymlink(String to, File from) throws ReflectiveOperationException {
         Reflect.invokeMethod(mLibcoreOs, "symlink", to, from.getAbsolutePath());
     }
@@ skipping 15 matching lines @@
         Object[] entries = new Object[files.length];
         File emptyDir = new File("");
         for (int i = 0; i < files.length; ++i) {
             File file = files[i];
             Object dexFile = Reflect.invokeMethod(clazz, "loadDexFile", file, optimizedDirectory);
             entries[i] = Reflect.newInstance(entryClazz, emptyDir, false, file, dexFile);
         }
         return entries;
     }
 }