Orderfile: Simplify prefetch logic.

The current logic in library_loader_hooks.cc for when to fork and
prefetch the native library has gotten complicated. This CL simplifies
it to current best practice: The prefetching is always done, restricted
to the ordered code if --orderfile-memory-optimization is set.

Bug: 758566
Change-Id: I86ecfff37b18eb7bda1edadfa5399db97b8be53e
Reviewed-on: https://chromium-review.googlesource.com/1095256Reviewed-by: Gabriel Charette <gab@chromium.org>
Reviewed-by: Benoit L <lizeb@chromium.org>
Commit-Queue: Matthew Cary <mattcary@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567274}

base/android/library_loader/library_loader_hooks.cc

@@ -211,13 +211,8 @@ static void JNI_LibraryLoader_ForkAndPrefetchNativeLibrary(
     JNIEnv* env,
     const JavaParamRef<jclass>& clazz) {
 #if BUILDFLAG(SUPPORTS_CODE_ORDERING)
-  if (!ShouldDoOrderfileMemoryOptimization() ||
-      CommandLine::ForCurrentProcess()->HasSwitch(
-          switches::kForceNativePrefetch)) {
-    NativeLibraryPrefetcher::ForkAndPrefetchNativeLibrary(
-        CommandLine::ForCurrentProcess()->HasSwitch(
-            switches::kNativePrefetchOrderedOnly));
-  }
+  return NativeLibraryPrefetcher::ForkAndPrefetchNativeLibrary(
+      ShouldDoOrderfileMemoryOptimization());
 #endif
 }
 

base/base_switches.cc

@@ -116,12 +116,6 @@ const char kEnableCrashReporterForTesting[] =
 // given in base/android/library_loader/anchor_functions.h, via madvise and
 // changing the library prefetch behavior.
 const char kOrderfileMemoryOptimization[] = "orderfile-memory-optimization";
-// Force prefetching of the native library even if otherwise disabled, eg by
-// --orderfile-memory-optimization.
-const char kForceNativePrefetch[] = "force-native-prefetch";
-// If prefetching is enabled, only prefetch the ordered part of the native
-// library. Has no effect if prefetching is disabled.
-const char kNativePrefetchOrderedOnly[] = "native-prefetch-ordered-only";
 #endif
 
 }  // namespace switches

base/base_switches.h

@@ -44,8 +44,6 @@ extern const char kEnableCrashReporterForTesting[];
 
 #if defined(OS_ANDROID)
 extern const char kOrderfileMemoryOptimization[];
-extern const char kForceNativePrefetch[];
-extern const char kNativePrefetchOrderedOnly[];
 #endif
 
 }  // namespace switches