Allow startup with missing V8 snapshot file.

content/app/content_main_runner.cc

Index: content/app/content_main_runner.cc
diff --git a/content/app/content_main_runner.cc b/content/app/content_main_runner.cc
index 279536b09b983deec9ae5f22856e5c0bbb72f83a..3fc6e83c159dc3cc0088adeef86171295d86b9a9 100644
--- a/content/app/content_main_runner.cc
+++ b/content/app/content_main_runner.cc
@@ -728,17 +728,23 @@ class ContentMainRunnerImpl : public ContentMainRunner {
 #endif  // !OS_ANDROID
     int v8_natives_fd = g_fds->MaybeGet(kV8NativesDataDescriptor);
     int v8_snapshot_fd = g_fds->MaybeGet(kV8SnapshotDataDescriptor);
-    if (v8_natives_fd != -1 && v8_snapshot_fd != -1) {
-      auto v8_natives_region = g_fds->GetRegion(kV8NativesDataDescriptor);
+    if (v8_snapshot_fd != -1) {
       auto v8_snapshot_region = g_fds->GetRegion(kV8SnapshotDataDescriptor);
       CHECK(gin::V8Initializer::LoadV8SnapshotFromFD(
-          v8_natives_fd, v8_natives_region.offset, v8_natives_region.size,
           v8_snapshot_fd, v8_snapshot_region.offset, v8_snapshot_region.size));
     } else {
-      CHECK(gin::V8Initializer::LoadV8Snapshot());
+      gin::V8Initializer::LoadV8Snapshot();
+    }
+    if (v8_natives_fd != -1) {
+      auto v8_natives_region = g_fds->GetRegion(kV8NativesDataDescriptor);
+      CHECK(gin::V8Initializer::LoadV8SnapshotFromFD(
+          v8_natives_fd, v8_natives_region.offset, v8_natives_region.size));
+    } else {
+      CHECK(gin::V8Initializer::LoadV8Natives());
     }
 #else
-    CHECK(gin::V8Initializer::LoadV8Snapshot());
+    gin::V8Initializer::LoadV8Snapshot();

[rmcilroy, 2015/06/01 14:06:31]

Maybe we should make it obvious from the function name that this is OK to fail?
Or maybe just return true if it fails in a way we expect (i.e., file is not
available) and only return false for unexpected errors (e.g., map errors on a
file which exists? Then you could CHECK it everytime?

[Erik Corry Chromium.org, 2015/06/02 11:18:52]

Not sure I want to CHECK it.  Lets say it's there, but can't be mapped or
verified.  I think it's more helpful to log it in UMA and carry on.

[rmcilroy, 2015/06/02 11:27:07]

As discussed below, let's get rid of the return values.

+    CHECK(gin::V8Initializer::LoadV8Natives());
 #endif  // OS_POSIX && !OS_MACOSX
 #endif  // V8_USE_EXTERNAL_STARTUP_DATA