mmap V8 snapshot and ICU data file in the android_webview

This makes it possible to mmap the V8 snapshot and ICU data file
directly from the WebView APK.
Doing so makes it possible to remove the android_webview_telemetry_build
flag which in turns means we can build the WebView with the same
set of flags that Chrome on Android uses.

BUG=442338

Review URL: https://codereview.chromium.org/812393002

Cr-Commit-Position: refs/heads/master@{#310765}

2 files changed, 60 insertions, 14 deletions

diff --git a/gin/isolate_holder.cc b/gin/isolate_holder.cc
index 38215b2..ab18ce4 100644
--- a/gin/isolate_holder.cc
+++ b/gin/isolate_holder.cc
@@ -11,6 +11,7 @@
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
 #include "base/rand_util.h"
+#include "base/strings/sys_string_conversions.h"
 #include "base/sys_info.h"
 #include "crypto/sha2.h"
 #include "gin/array_buffer.h"
@@ -42,15 +43,23 @@ base::MemoryMappedFile* g_mapped_natives = NULL;
 base::MemoryMappedFile* g_mapped_snapshot = NULL;
 
 #if defined(V8_USE_EXTERNAL_STARTUP_DATA)
-bool MapV8Files(base::FilePath* natives_path, base::FilePath* snapshot_path,
-                int natives_fd = -1, int snapshot_fd = -1) {
+bool MapV8Files(base::FilePath* natives_path,
+                base::FilePath* snapshot_path,
+                int natives_fd = -1,
+                int snapshot_fd = -1,
+                base::MemoryMappedFile::Region natives_region =
+                    base::MemoryMappedFile::Region::kWholeFile,
+                base::MemoryMappedFile::Region snapshot_region =
+                    base::MemoryMappedFile::Region::kWholeFile) {
   int flags = base::File::FLAG_OPEN | base::File::FLAG_READ;
 
   g_mapped_natives = new base::MemoryMappedFile;
   if (!g_mapped_natives->IsValid()) {
     if (natives_fd == -1
-        ? !g_mapped_natives->Initialize(base::File(*natives_path, flags))
-        : !g_mapped_natives->Initialize(base::File(natives_fd))) {
+            ? !g_mapped_natives->Initialize(base::File(*natives_path, flags),
+                                            natives_region)
+            : !g_mapped_natives->Initialize(base::File(natives_fd),
+                                            natives_region)) {
       delete g_mapped_natives;
       g_mapped_natives = NULL;
       LOG(FATAL) << "Couldn't mmap v8 natives data file";
@@ -61,8 +70,10 @@ bool MapV8Files(base::FilePath* natives_path, base::FilePath* snapshot_path,
   g_mapped_snapshot = new base::MemoryMappedFile;
   if (!g_mapped_snapshot->IsValid()) {
     if (snapshot_fd == -1
-        ? !g_mapped_snapshot->Initialize(base::File(*snapshot_path, flags))
-        : !g_mapped_snapshot->Initialize(base::File(snapshot_fd))) {
+            ? !g_mapped_snapshot->Initialize(base::File(*snapshot_path, flags),
+                                             snapshot_region)
+            : !g_mapped_snapshot->Initialize(base::File(snapshot_fd),
+                                             snapshot_region)) {
       delete g_mapped_snapshot;
       g_mapped_snapshot = NULL;
       LOG(ERROR) << "Couldn't mmap v8 snapshot data file";
@@ -106,6 +117,9 @@ extern const unsigned char g_natives_fingerprint[];
 extern const unsigned char g_snapshot_fingerprint[];
 #endif  // V8_VERIFY_EXTERNAL_STARTUP_DATA
 
+const char IsolateHolder::kNativesFileName[] = "natives_blob.bin";
+const char IsolateHolder::kSnapshotFileName[] = "snapshot_blob.bin";
+
 // static
 bool IsolateHolder::LoadV8Snapshot() {
   if (g_mapped_natives && g_mapped_snapshot)
@@ -116,13 +130,17 @@ bool IsolateHolder::LoadV8Snapshot() {
   PathService::Get(v8_snapshot_dir, &data_path);
   DCHECK(!data_path.empty());
 
-  base::FilePath natives_path = data_path.AppendASCII("natives_blob.bin");
-  base::FilePath snapshot_path = data_path.AppendASCII("snapshot_blob.bin");
+  base::FilePath natives_path = data_path.AppendASCII(kNativesFileName);
+  base::FilePath snapshot_path = data_path.AppendASCII(kSnapshotFileName);
 #else  // !defined(OS_MACOSX)
+  base::ScopedCFTypeRef<CFStringRef> natives_file_name(
+      base::SysUTF8ToCFStringRef(kNativesFileName));
   base::FilePath natives_path = base::mac::PathForFrameworkBundleResource(
-      CFSTR("natives_blob.bin"));
+      natives_file_name);
+  base::ScopedCFTypeRef<CFStringRef> snapshot_file_name(
+      base::SysUTF8ToCFStringRef(kSnapshotFileName));
   base::FilePath snapshot_path = base::mac::PathForFrameworkBundleResource(
-      CFSTR("snapshot_blob.bin"));
+      snapshot_file_name);
   DCHECK(!natives_path.empty());
   DCHECK(!snapshot_path.empty());
 #endif  // !defined(OS_MACOSX)
@@ -139,11 +157,31 @@ bool IsolateHolder::LoadV8Snapshot() {
 }
 
 //static
-bool IsolateHolder::LoadV8SnapshotFD(int natives_fd, int snapshot_fd) {
+bool IsolateHolder::LoadV8SnapshotFd(int natives_fd,
+                               int64 natives_offset,
+                               int64 natives_size,
+                               int snapshot_fd,
+                               int64 snapshot_offset,
+                               int64 snapshot_size) {
   if (g_mapped_natives && g_mapped_snapshot)
     return true;
 
-  return MapV8Files(NULL, NULL, natives_fd, snapshot_fd);
+  base::MemoryMappedFile::Region natives_region =
+      base::MemoryMappedFile::Region::kWholeFile;
+  if (natives_size != 0 || natives_offset != 0) {
+    natives_region =
+        base::MemoryMappedFile::Region(natives_offset, natives_size);
+  }
+
+  base::MemoryMappedFile::Region snapshot_region =
+      base::MemoryMappedFile::Region::kWholeFile;
+  if (natives_size != 0 || natives_offset != 0) {
+    snapshot_region =
+        base::MemoryMappedFile::Region(snapshot_offset, snapshot_size);
+  }
+
+  return MapV8Files(
+      NULL, NULL, natives_fd, snapshot_fd, natives_region, snapshot_region);
 }
 #endif  // V8_USE_EXTERNAL_STARTUP_DATA
 
diff --git a/gin/public/isolate_holder.h b/gin/public/isolate_holder.h
index 64fc952..44d1d89 100644
--- a/gin/public/isolate_holder.h
+++ b/gin/public/isolate_holder.h
@@ -33,7 +33,7 @@ class GIN_EXPORT IsolateHolder {
   // Should be invoked once before creating IsolateHolder instances to
   // initialize V8 and Gin. In case V8_USE_EXTERNAL_STARTUP_DATA is defined,
   // V8's initial snapshot should be loaded (by calling LoadV8Snapshot or
-  // LoadV8SnapshotFD) before calling Initialize.
+  // LoadV8SnapshotFd) before calling Initialize.
   static void Initialize(ScriptMode mode,
                          v8::ArrayBuffer::Allocator* allocator);
 
@@ -52,7 +52,15 @@ class GIN_EXPORT IsolateHolder {
   void RemoveRunMicrotasksObserver();
 
 #if defined(V8_USE_EXTERNAL_STARTUP_DATA)
-  static bool LoadV8SnapshotFD(int natives_fd, int snapshot_fd);
+  static const char kNativesFileName[];
+  static const char kSnapshotFileName[];
+
+  static bool LoadV8SnapshotFd(int natives_fd,
+                               int64 natives_offset,
+                               int64 natives_size,
+                               int snapshot_fd,
+                               int64 snapshot_offset,
+                               int64 snapshot_size);
   static bool LoadV8Snapshot();
 #endif  // V8_USE_EXTERNAL_STARTUP_DATA
   static void GetV8ExternalSnapshotData(const char** natives_data_out,