Reland^2: [PA] Enable PA-E on Linux component build.

PS1 = the reverted CL: https://chromium-review.googlesource.com/c/chromium/src/+/4357306

The difference between the reverted one and this CL is:
- disable PartitionAlloc-As-Malloc when is_component_build=true and
  is_debug=true.

PartitionAlloc-As-Malloc made browser_tests, interactive_ui_tests,...
running on Linux Dbg(1) bot slower, and caused lots of timeout failures.

Since the debug bots(*)' gn args have both is_debug=true and
is_component_build=true, PartitionAlloc-As-Malloc didn't affect the
debug bots. But the reverted CL enabled PartitionAlloc-As-Malloc on
the bots.
(*) Linux Builder (dbg), cast Linux Debug, and Linux Tests (dbg)(1).

Change-Id: I0d37f66f7bcac01a209531305df883821f79b354

Cq-Include-Trybots: luci.chromium.try:linux_chromium_dbg_ng
Change-Id: I0d37f66f7bcac01a209531305df883821f79b354
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4378189
Commit-Queue: Takashi Sakamoto <tasak@google.com>
Reviewed-by: Bartek Nowierski <bartekn@chromium.org>
Reviewed-by: Bo Liu <boliu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1124633}

base/allocator/partition_alloc_support.cc

@@ -827,6 +827,11 @@ void ReconfigurePartitionForKnownProcess(const std::string& process_type) {
   // experiments.
 }
 
+PartitionAllocSupport* PartitionAllocSupport::Get() {
+  static auto* singleton = new PartitionAllocSupport();
+  return singleton;
+}
+
 PartitionAllocSupport::PartitionAllocSupport() = default;
 
 void PartitionAllocSupport::ReconfigureForTests() {

base/allocator/partition_alloc_support.h

@@ -91,10 +91,7 @@ class BASE_EXPORT PartitionAllocSupport {
       std::string stacktrace);
 #endif
 
-  static PartitionAllocSupport* Get() {
-    static auto* singleton = new PartitionAllocSupport();
-    return singleton;
-  }
+  static PartitionAllocSupport* Get();
 
   static BrpConfiguration GetBrpConfiguration(const std::string& process_type);
 

base/allocator/partition_allocator/partition_root.h

@@ -1052,6 +1052,7 @@ enum class PtrPosWithinAlloc {
 //
 // This isn't a general purpose function. The caller is responsible for ensuring
 // that the ref-count is in place for this allocation.
+PA_COMPONENT_EXPORT(PARTITION_ALLOC)
 PtrPosWithinAlloc IsPtrWithinSameAlloc(uintptr_t orig_address,
                                        uintptr_t test_address,
                                        size_t type_size);

build_overrides/partition_alloc.gni

@@ -34,11 +34,17 @@ if (is_ios) {
 # Sanitizers replace the allocator, don't use our own.
 _is_using_sanitizers = is_asan || is_hwasan || is_lsan || is_tsan || is_msan
 
-# - Component build support is disabled on all platforms. It is known to cause
-#   issues on some (e.g. Windows with shims, Android with non-universal symbol
-#   wrapping), and has not been validated on others.
+# - Component build support is disabled on all platforms except Linux. It is
+#   known to cause issues on some (e.g. Windows with shims, Android with
+#   non-universal symbol wrapping), and has not been validated on others.
+# - Disable on Linux when component and debug build are used together, because
+#   PA-E caused lots of timeouts on Linux Tests(dbg).
+#   TODO(crbug.com/1429450): fix the timeout issue and enable on linux debug
+#   and component build.
 # - Windows: debug CRT is not compatible, see below.
-_disable_partition_alloc_everywhere = is_component_build || (is_win && is_debug)
+_disable_partition_alloc_everywhere =
+    (is_linux && is_component_build && is_debug) ||
+    (!is_linux && is_component_build) || (is_win && is_debug)
 
 # - NaCl: No plans to support it.
 # - iOS: Depends on ios_partition_alloc_enabled.

content/browser/web_contents/web_contents_impl_browsertest.cc

@@ -7,6 +7,7 @@
 #include <utility>
 #include <vector>
 
+#include "base/allocator/partition_alloc_features.h"
 #include "base/allocator/partition_allocator/partition_alloc_buildflags.h"
 #include "base/command_line.h"
 #include "base/containers/contains.h"
@@ -5926,7 +5927,24 @@ class PCScanFeature {
 // Initialize PCScanFeature before WebContentsImplBrowserTest to make sure that
 // the feature is enabled within the entire lifetime of the test.
 class WebContentsImplStarScanBrowserTest : private PCScanFeature,
-                                           public WebContentsImplBrowserTest {};
+                                           public WebContentsImplBrowserTest {
+ public:
+  void SetUp() override {
+    // Since ReconfigureAfterFeatureListInit() has been already invoked at
+    // FeatureListScopedToEachTest::OnTestStart(), we cannot enable PCScan
+    // and cannot re-reconfigure partition roots here. This causes DCHECK()
+    // failure at PerfromcScan().
+    if (!base::FeatureList::IsEnabled(base::features::kPartitionAllocPCScan) &&
+        !base::FeatureList::IsEnabled(
+            base::features::kPartitionAllocPCScanBrowserOnly) &&
+        !base::FeatureList::IsEnabled(
+            base::features::kPartitionAllocPCScanRendererOnly)) {
+      GTEST_SKIP() << "PCScanFeature is not enabled. Need --enable-features"
+                   << "=PartitionAllocPCScan";
+    }
+    WebContentsImplBrowserTest::SetUp();
+  }
+};
 
 }  // namespace