tools/gn: sync documentation with reality

Compiler tool definitions use {{source}} and {{output}} to specify the
source and output files, not $in and $out.

Also fix some typos and spurious commas.

Review URL: https://codereview.chromium.org/1020073002

Cr-Commit-Position: refs/heads/master@{#321605}

tools/gn/function_toolchain.cc

@@ -266,7 +266,7 @@ const char kToolchain_Help[] =
     "    concurrent_links = 8\n"
     "\n"
     "    tool(\"cc\") {\n"
-    "      command = \"gcc $in\"\n"
+    "      command = \"gcc {{source}}\"\n"
     "      ...\n"
     "    }\n"
     "\n"
@@ -553,7 +553,7 @@ const char kTool_Help[] =
     "        will be included for targets in other toolchains.\n"
     "\n"
     "    {{output}}\n"
-    "        The relative path and name of the output)((s) of the current\n"
+    "        The relative path and name of the output(s) of the current\n"
     "        build step. If there is more than one output, this will expand\n"
     "        to a list of all of them.\n"
     "        Example: \"out/base/my_file.o\"\n"
@@ -631,7 +631,7 @@ const char kTool_Help[] =
     "    {{ldflags}}\n"
     "        Expands to the processed set of ldflags and library search paths\n"
     "        specified for the target.\n"
-    "        Example: \"-m64, -fPIC -pthread -L/usr/local/mylib\"\n"
+    "        Example: \"-m64 -fPIC -pthread -L/usr/local/mylib\"\n"
     "\n"
     "    {{libs}}\n"
     "        Expands to the list of system libraries to link to. Each will\n"
@@ -688,10 +688,10 @@ const char kTool_Help[] =
                  "{{output_extension}}.TOC\",\n"
     "      ]\n"
     "      link_output =\n"
-    "        \"{{root_out_dir}}/{{target_output_name}}{{output_extension}}\",\n"
+    "        \"{{root_out_dir}}/{{target_output_name}}{{output_extension}}\"\n"
     "      depend_output =\n"
     "        \"{{root_out_dir}}/{{target_output_name}}"
-                 "{{output_extension}}.TOC\",\n"
+                 "{{output_extension}}.TOC\"\n"
     "      restat = true\n"
     "    }\n"
     "\n"
@@ -703,14 +703,14 @@ const char kTool_Help[] =
     "    lib_dir_prefix = \"-L\"\n"
     "\n"
     "    tool(\"cc\") {\n"
-    "      command = \"gcc \\$in -o \\$out\"\n"
-    "      outputs = [ \"{{source_out_dir}}/{{source_name_part}}.o\"\n"
-    "      description = \"GCC \\$in\"\n"
+    "      command = \"gcc {{source}} -o {{output}}\"\n"
+    "      outputs = [ \"{{source_out_dir}}/{{source_name_part}}.o\" ]\n"
+    "      description = \"GCC {{source}}\"\n"
     "    }\n"
     "    tool(\"cxx\") {\n"
-    "      command = \"g++ \\$in -o \\$out\"\n"
-    "      outputs = [ \"{{source_out_dir}}/{{source_name_part}}.o\"\n"
-    "      description = \"G++ \\$in\"\n"
+    "      command = \"g++ {{source}} -o {{output}}\"\n"
+    "      outputs = [ \"{{source_out_dir}}/{{source_name_part}}.o\" ]\n"
+    "      description = \"G++ {{source}}\"\n"
     "    }\n"
     "  }\n";