[api] Assume that v8/include is in the include path for all public headers

Probably easier to use for embedders.

BUG=
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/1749663002

Cr-Commit-Position: refs/heads/master@{#34357}

BUILD.gn

@@ -77,6 +77,11 @@ config("internal_config_base") {
   include_dirs = [ "." ]
 }
 
+# This config should be applied to code using the libplatform.
+config("libplatform_config") {
+  include_dirs = [ "include" ]
+}
+
 # This config should only be applied to code using V8 and not any V8 code
 # itself.
 config("external_config") {
@@ -1865,6 +1870,7 @@ if (current_toolchain == snapshot_toolchain) {
     configs += [ "//build/config/compiler:no_chromium_code" ]
     configs += [
       ":internal_config",
+      ":libplatform_config",
       ":features",
       ":toolchain",
     ]
@@ -1977,6 +1983,7 @@ source_set("json_fuzzer") {
   configs += [ "//build/config/compiler:no_chromium_code" ]
   configs += [
     ":internal_config",
+    ":libplatform_config",
     ":features",
     ":toolchain",
   ]
@@ -1995,6 +2002,7 @@ source_set("parser_fuzzer") {
   configs += [ "//build/config/compiler:no_chromium_code" ]
   configs += [
     ":internal_config",
+    ":libplatform_config",
     ":features",
     ":toolchain",
   ]
@@ -2013,6 +2021,7 @@ source_set("regexp_fuzzer") {
   configs += [ "//build/config/compiler:no_chromium_code" ]
   configs += [
     ":internal_config",
+    ":libplatform_config",
     ":features",
     ":toolchain",
   ]

include/libplatform/libplatform.h

@@ -5,7 +5,7 @@
 #ifndef V8_LIBPLATFORM_LIBPLATFORM_H_
 #define V8_LIBPLATFORM_LIBPLATFORM_H_
 
-#include "include/v8-platform.h"
+#include "v8-platform.h"  // NOLINT(build/include)
 
 namespace v8 {
 namespace platform {

include/v8-experimental.h

@@ -10,7 +10,7 @@
 #ifndef V8_INCLUDE_V8_EXPERIMENTAL_H_
 #define V8_INCLUDE_V8_EXPERIMENTAL_H_
 
-#include "include/v8.h"
+#include "v8.h"  // NOLINT(build/include)
 
 namespace v8 {
 namespace experimental {

tools/gyp/v8.gyp

@@ -1912,6 +1912,11 @@
           'toolsets': ['target'],
         }],
       ],
+      'direct_dependent_settings': {
+        'include_dirs': [
+          '../../include',
+        ],
+      },
     },
     {
       'target_name': 'natives_blob',