Remove unnecessary deps on libc++

Also:
* Add no_default_deps to mini_installer.
* Updates an incorrect comment and removes an unnecessary dependency on
  libc++ in mini_installer/BUILD.gn which became broken in [1].

[1] https://chromium-review.googlesource.com/1073613

BUG=None

Change-Id: I44f8f09e36f2764b3077af5d0cd7605a575b347e
Reviewed-on: https://chromium-review.googlesource.com/1157509
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579879}

chrome/installer/mini_installer/BUILD.gn

@@ -270,17 +270,18 @@ template("generate_mini_installer") {
     ]
 
     # In general, mini_installer tries to avoid depending on the C++ standard
-    # library for size reasons. This is achieved by setting a custom entry point
-    # (which avoids pulling in the standard library via a link dependency) as
-    # well as by not depending on //buildtools/third_party/libc++.
+    # library for size reasons. This is achieved by:
+    #   1. setting a custom entry point which avoids pulling in the standard
+    #      library via a link dependency.
+    #   2. setting no_default_deps=true to avoid including the implicit
+    #      dependency on //buildtools/third_party/libc++ in builds that set
+    #      use_custom_libcxx=true.
     #
     # But in asan builds we need to link against the asan runtime library, which
     # in turn depends on the standard library and relies on it to run
-    # initializers. So in asan builds we depend on libc++ for the asan runtime
-    # and use the standard entry point.
-    if (is_asan) {
-      deps += [ "//buildtools/third_party/libc++" ]
-    } else {
+    # initializers.
+    if (!is_asan) {
+      no_default_deps = true
       ldflags += [ "/ENTRY:MainEntryPoint" ]
     }
   }

tools/v8_context_snapshot/BUILD.gn

@@ -106,11 +106,6 @@ if (use_v8_context_snapshot) {
       "//v8",
     ]
 
-    if (is_linux && (is_component_build || using_sanitizer) &&
-        use_custom_libcxx) {
-      deps += [ "//buildtools/third_party/libc++:libc++" ]
-    }
-
     configs += [
       "//v8:external_startup_data",
       ":disable_icf",